Find, fix and prevent vulnerabilities in your code.
high severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Deserialization of Untrusted Data via the MemCacheStore
and RedisCacheStore
. when
untrusted user input is written to the cache store using the raw: true
parameter, re-reading the result
from the cache can evaluate the user input as a Marshalled object instead of plain text.
Remediation
Upgrade activesupport
to version 5.2.4.3, 6.0.3.1 or higher.
References
high severity
- Vulnerable module: addressable
- Introduced through: http@2.0.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › http@2.0.3 › addressable@2.4.0Remediation: Upgrade to http@2.0.3.
Overview
addressable is an is an alternative implementation to the URI implementation that is part of Ruby's standard library.
Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) within the URI template implementation. A maliciously crafted template may result in uncontrolled resource consumption.
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.
The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.
Let’s take the following regular expression as an example:
regex = /A(B|C+)+D/
This regular expression accomplishes the following:
A
The string must start with the letter 'A'(B|C+)+
The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the+
matches one or more times). The+
at the end of this section states that we can look for one or more matches of this section.D
Finally, we ensure this section of the string ends with a 'D'
The expression would match inputs such as ABBD
, ABCCCCD
, ABCBCCCD
and ACCCCCD
It most cases, it doesn't take very long for a regex engine to find a match:
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total
The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.
Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.
Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:
- CCC
- CC+C
- C+CC
- C+C+C.
The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.
From there, the number of steps the engine must use to validate a string just continues to grow.
String | Number of C's | Number of steps |
---|---|---|
ACCCX | 3 | 38 |
ACCCCX | 4 | 71 |
ACCCCCX | 5 | 136 |
ACCCCCCCCCCCCCCX | 14 | 65,553 |
By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.
Remediation
Upgrade addressable
to version 2.8.0 or higher.
References
high severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport
is toolkit of support libraries and Ruby core extensions extracted from the Rails framework
Ruby on Rails contains a flaw in the JSON parser which may allow a remote attacker to bypass restrictions, allowing them to bypass authentication systems, inject arbitrary SQL, inject and execute arbitrary code, or perform a DoS attack on a Rails application.
Details
Rails supports multiple parsing backends, one of which involves transforming JSON into YAML via the YAML parser. With a specially crafted payload, an attacker can subvert the backend into decoding a subset of YAML. This may allow a remote attacker to bypass restrictions, allowing them to bypass authentication systems, inject arbitrary SQL, inject and execute arbitrary code, or perform a DoS attack on a Rails application.
References
high severity
- Vulnerable module: rake
- Introduced through: rake@0.9.2 and govuk-lint@1.2.0
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › rake@0.9.2Remediation: Upgrade to rake@12.3.3.
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › govuk-lint@1.2.0 › scss_lint@0.49.0 › rake@0.9.2Remediation: Upgrade to govuk-lint@1.2.0.
Overview
rake is a Make-like program implemented in Ruby.
Affected versions of this package are vulnerable to Arbitrary Code Injection in Rake::FileList
when supplying a filename that begins with the pipe character |
.
PoC by Katsuhiko Yoshida
% ls -1
Gemfile
Gemfile.lock
poc_rake.rb
vendor
| touch evil.txt
% bundle exec ruby poc_rake.rb
["poc_rake.rb", "Gemfile", "Gemfile.lock", "| touch evil.txt", "vendor"]
poc_rake.rb:6:list.egrep(/something/)
Error while processing 'vendor': Is a directory @ io_fillbuf - fd:7 vendor
% ls -1
Gemfile
Gemfile.lock
evil.txt
poc_rake.rb
vendor
| touch evil.txt
Remediation
Upgrade rake
to version 12.3.3 or higher.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Cross-site Scripting (XSS) when using the SafeBuffer#bytesplice()
function, the output of which is not treated as mutated and therefore improperly tagged as html_safe
although it may contain executable scripts.
Workaround
Avoid calling bytesplice
on a SafeBuffer (html_safe)
string with untrusted user input.
Details
A cross-site scripting attack occurs when the attacker tricks a legitimate web-based application or site to accept a request as originating from a trusted source.
This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.
Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.
Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, <
can be coded as <
; and >
can be coded as >
; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses <
and >
as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.
The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.
Types of attacks
There are a few methods by which XSS can be manipulated:
Type | Origin | Description |
---|---|---|
Stored | Server | The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link. |
Reflected | Server | The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser. |
DOM-based | Client | The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data. |
Mutated | The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters. |
Affected environments
The following environments are susceptible to an XSS attack:
- Web servers
- Application servers
- Web application environments
How to prevent
This section describes the top best practices designed to specifically protect your code:
- Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
- Convert special characters such as
?
,&
,/
,<
,>
and spaces to their respective HTML or URL encoded equivalents. - Give users the option to disable client-side scripts.
- Redirect invalid requests.
- Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
- Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
- Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.
Remediation
Upgrade activesupport
to version 6.1.7.3, 7.0.4.3 or higher.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport
is toolkit of support libraries and Ruby core extensions extracted from the Rails framework
Affected versions of this package are vulnerable to Denial of Service (Dos) attacks. The ActiveSupport XML parsing functionality supports multiple pluggable backends. One backend supported for JRuby users is ActiveSupport::XmlMini_JDOM
which makes use of the javax.xml.parsers.DocumentBuilder
class. In some JVM configurations the default settings of that class can allow an attacker to construct XML which may allow for various denial of service attacks.
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.
Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.
One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.
When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.
Two common types of DoS vulnerabilities:
High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.
Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm
ws
package
Remediation
Upgrade activesupport
to versions 2.3.0, 3.1.12, 3.2.13 or higher.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport
is toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Denial of Service (DoS). Specially crafted XML documents can cause applications to raise a SystemStackError
. This only impacts applications using REXML or JDOM as their XML processor. Other XML processors that Rails supports are not impacted.
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its intended and legitimate users.
Unlike other vulnerabilities, DoS attacks usually do not aim at breaching security. Rather, they are focused on making websites and services unavailable to genuine users resulting in downtime.
One popular Denial of Service vulnerability is DDoS (a Distributed Denial of Service), an attack that attempts to clog network pipes to the system by generating a large volume of traffic from many machines.
When it comes to open source libraries, DoS vulnerabilities allow attackers to trigger such a crash or crippling of the service by using a flaw either in the application code or from the use of open source libraries.
Two common types of DoS vulnerabilities:
High CPU/Memory Consumption- An attacker sending crafted requests that could cause the system to take a disproportionate amount of time to process. For example, commons-fileupload:commons-fileupload.
Crash - An attacker sending crafted requests that could cause the system to crash. For Example, npm
ws
package
Remediation
Upgrade activesupport
to versions 4.1.11, 4.2.2, 4.2.22 or higher.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Regular Expression Denial of Service (ReDoS) in the underscore()
function in inflector/methods.rb
. This affects String#underscore
, ActiveSupport::Inflector.underscore
, String#titleize
, and any other methods using these.
NOTE: The impact of this vulnerability may be mitigated by configuring Regexp.timeout
. Additionally, patches have been released to address this issue: 6-1-Avoid-regex-backtracking-in-Inflector.underscore.patch, 7-0-Avoid-regex-backtracking-in-Inflector.underscore.patch
Details
Denial of Service (DoS) describes a family of attacks, all aimed at making a system inaccessible to its original and legitimate users. There are many types of DoS attacks, ranging from trying to clog the network pipes to the system by generating a large volume of traffic from many machines (a Distributed Denial of Service - DDoS - attack) to sending crafted requests that cause a system to crash or take a disproportional amount of time to process.
The Regular expression Denial of Service (ReDoS) is a type of Denial of Service attack. Regular expressions are incredibly powerful, but they aren't very intuitive and can ultimately end up making it easy for attackers to take your site down.
Let’s take the following regular expression as an example:
regex = /A(B|C+)+D/
This regular expression accomplishes the following:
A
The string must start with the letter 'A'(B|C+)+
The string must then follow the letter A with either the letter 'B' or some number of occurrences of the letter 'C' (the+
matches one or more times). The+
at the end of this section states that we can look for one or more matches of this section.D
Finally, we ensure this section of the string ends with a 'D'
The expression would match inputs such as ABBD
, ABCCCCD
, ABCBCCCD
and ACCCCCD
It most cases, it doesn't take very long for a regex engine to find a match:
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCD")'
0.04s user 0.01s system 95% cpu 0.052 total
$ time node -e '/A(B|C+)+D/.test("ACCCCCCCCCCCCCCCCCCCCCCCCCCCCX")'
1.79s user 0.02s system 99% cpu 1.812 total
The entire process of testing it against a 30 characters long string takes around ~52ms. But when given an invalid string, it takes nearly two seconds to complete the test, over ten times as long as it took to test a valid string. The dramatic difference is due to the way regular expressions get evaluated.
Most Regex engines will work very similarly (with minor differences). The engine will match the first possible way to accept the current character and proceed to the next one. If it then fails to match the next one, it will backtrack and see if there was another way to digest the previous character. If it goes too far down the rabbit hole only to find out the string doesn’t match in the end, and if many characters have multiple valid regex paths, the number of backtracking steps can become very large, resulting in what is known as catastrophic backtracking.
Let's look at how our expression runs into this problem, using a shorter string: "ACCCX". While it seems fairly straightforward, there are still four different ways that the engine could match those three C's:
- CCC
- CC+C
- C+CC
- C+C+C.
The engine has to try each of those combinations to see if any of them potentially match against the expression. When you combine that with the other steps the engine must take, we can use RegEx 101 debugger to see the engine has to take a total of 38 steps before it can determine the string doesn't match.
From there, the number of steps the engine must use to validate a string just continues to grow.
String | Number of C's | Number of steps |
---|---|---|
ACCCX | 3 | 38 |
ACCCCX | 4 | 71 |
ACCCCCX | 5 | 136 |
ACCCCCCCCCCCCCCX | 14 | 65,553 |
By the time the string includes 14 C's, the engine has to take over 65,000 steps just to see if the string is valid. These extreme situations can cause them to work very slowly (exponentially related to input size, as shown above), allowing an attacker to exploit this and can cause the service to excessively consume CPU, resulting in a Denial of Service.
Remediation
Upgrade activesupport
to version 6.1.7.1, 7.0.4.1 or higher.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport
is toolkit of support libraries and Ruby core extensions extracted from the Rails frameworkץ
Affected versions of this package are vulnerable to Cross-site Scripting (XSS). The application does not validate direct manipulations of SafeBuffer objects via '[]' and other methods. This may allow a user to create a specially crafted request that would execute arbitrary script code in a user's browser within the trust relationship between their browser and the server.
Details
A cross-site scripting attack occurs when the attacker tricks a legitimate web-based application or site to accept a request as originating from a trusted source.
This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.
ֿInjecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.
Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, <
can be coded as <
; and >
can be coded as >
; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses <
and >
as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.
The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.
Types of attacks
There are a few methods by which XSS can be manipulated:
Type | Origin | Description |
---|---|---|
Stored | Server | The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link. |
Reflected | Server | The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser. |
DOM-based | Client | The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data. |
Mutated | The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters. |
Affected environments
The following environments are susceptible to an XSS attack:
- Web servers
- Application servers
- Web application environments
How to prevent
This section describes the top best practices designed to specifically protect your code:
- Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
- Convert special characters such as
?
,&
,/
,<
,>
and spaces to their respective HTML or URL encoded equivalents. - Give users the option to disable client-side scripts.
- Redirect invalid requests.
- Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
- Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
- Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport
is toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Cross-site Scripting. The HTML escaping code functionality does not properly escape a single quote character. This may allow a user to create a specially crafted request that would execute arbitrary script code in a user's browser within the trust relationship between their browser and the server.
Details
A cross-site scripting attack occurs when the attacker tricks a legitimate web-based application or site to accept a request as originating from a trusted source.
This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.
ֿInjecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.
Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, <
can be coded as <
; and >
can be coded as >
; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses <
and >
as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.
The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.
Types of attacks
There are a few methods by which XSS can be manipulated:
Type | Origin | Description |
---|---|---|
Stored | Server | The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link. |
Reflected | Server | The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser. |
DOM-based | Client | The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data. |
Mutated | The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters. |
Affected environments
The following environments are susceptible to an XSS attack:
- Web servers
- Application servers
- Web application environments
How to prevent
This section describes the top best practices designed to specifically protect your code:
- Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
- Convert special characters such as
?
,&
,/
,<
,>
and spaces to their respective HTML or URL encoded equivalents. - Give users the option to disable client-side scripts.
- Redirect invalid requests.
- Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
- Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
- Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.
References
medium severity
- Vulnerable module: activesupport
- Introduced through: whenever@0.7.3
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › whenever@0.7.3 › activesupport@3.0.8Remediation: Upgrade to whenever@0.7.3.
Overview
activesupport is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework.
Affected versions of this package are vulnerable to Cross-site Scripting (XSS). activesupport/lib/active_support/core_ext/string/output_safety.rb
allows remote attackers to inject arbitrary web script or HTML via a malformed Unicode string, related to a "UTF-8 escaping vulnerability."
Details
A cross-site scripting attack occurs when the attacker tricks a legitimate web-based application or site to accept a request as originating from a trusted source.
This is done by escaping the context of the web application; the web application then delivers that data to its users along with other trusted dynamic content, without validating it. The browser unknowingly executes malicious script on the client side (through client-side languages; usually JavaScript or HTML) in order to perform actions that are otherwise typically blocked by the browser’s Same Origin Policy.
Injecting malicious code is the most prevalent manner by which XSS is exploited; for this reason, escaping characters in order to prevent this manipulation is the top method for securing code against this vulnerability.
Escaping means that the application is coded to mark key characters, and particularly key characters included in user input, to prevent those characters from being interpreted in a dangerous context. For example, in HTML, <
can be coded as <
; and >
can be coded as >
; in order to be interpreted and displayed as themselves in text, while within the code itself, they are used for HTML tags. If malicious content is injected into an application that escapes special characters and that malicious content uses <
and >
as HTML tags, those characters are nonetheless not interpreted as HTML tags by the browser if they’ve been correctly escaped in the application code and in this way the attempted attack is diverted.
The most prominent use of XSS is to steal cookies (source: OWASP HttpOnly) and hijack user sessions, but XSS exploits have been used to expose sensitive information, enable access to privileged services and functionality and deliver malware.
Types of attacks
There are a few methods by which XSS can be manipulated:
Type | Origin | Description |
---|---|---|
Stored | Server | The malicious code is inserted in the application (usually as a link) by the attacker. The code is activated every time a user clicks the link. |
Reflected | Server | The attacker delivers a malicious link externally from the vulnerable web site application to a user. When clicked, malicious code is sent to the vulnerable web site, which reflects the attack back to the user’s browser. |
DOM-based | Client | The attacker forces the user’s browser to render a malicious page. The data in the page itself delivers the cross-site scripting data. |
Mutated | The attacker injects code that appears safe, but is then rewritten and modified by the browser, while parsing the markup. An example is rebalancing unclosed quotation marks or even adding quotation marks to unquoted parameters. |
Affected environments
The following environments are susceptible to an XSS attack:
- Web servers
- Application servers
- Web application environments
How to prevent
This section describes the top best practices designed to specifically protect your code:
- Sanitize data input in an HTTP request before reflecting it back, ensuring all data is validated, filtered or escaped before echoing anything back to the user, such as the values of query parameters during searches.
- Convert special characters such as
?
,&
,/
,<
,>
and spaces to their respective HTML or URL encoded equivalents. - Give users the option to disable client-side scripts.
- Redirect invalid requests.
- Detect simultaneous logins, including those from two separate IP addresses, and invalidate those sessions.
- Use and enforce a Content Security Policy (source: Wikipedia) to disable any features that might be manipulated for an XSS attack.
- Read the documentation for any of the libraries referenced in your code to understand which elements allow for embedded HTML.
Remediation
Upgrade activesupport
to version 2.3.13, 3.0.10, 3.1.0.rc5 or higher.
References
low severity
- Vulnerable module: rubocop
- Introduced through: govuk-lint@1.2.0
Detailed paths
-
Introduced through: alphagov/govuk-app-deployment@alphagov/govuk-app-deployment#a8acf0a3e496c27dd0038913a848e5c25e2a8a78 › govuk-lint@1.2.0 › rubocop@0.39.0Remediation: Upgrade to govuk-lint@3.0.0.
Overview
RuboCop
is a ruby static code analyzer, based on the community Ruby style guide.
Affected version of the package store cache files in /tmp/$UID/rubocop_cache/
. Since there are no ownership checks, a malicious local users could exploit this to tamper with cache files belonging to other users.
Remediation
Upgrade RuboCop
to version 0.49 or higher.