Overview

connect is a stack of middleware that is executed in order in each request.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS). The methodOverride middleware allows the http post to override the method of the request with the value of the _method post key or with the header x-http-method-override.

Because the user post input was not checked, req.method could contain any kind of value. Because the req.method did not match any common method VERB, connect answered with a 404 page containing the "Cannot [method] [url]" content. The method was not properly encoded for output in the browser.

Example

~ curl "localhost:3000" -d "_method=<script src=http://nodesecurity.io/xss.js></script>"
Cannot <SCRIPT SRC=HTTP://NODESECURITY.IO/XSS.JS></SCRIPT> /

Mitigation factors

Update to version 2.8.2 or disable methodOverride. It is not possible to avoid the vulnerability if you have enabled this middleware in the top of your stack.

History

• (2013-06-27) Bug reported
• (2013-06-27) First fix: escape req.method output - v2.8.1
• (2013-06-27) Second fix: whitelist - v2.8.2

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 &lt; and > can be coded as &gt; 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:

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 connect to version 2.8.2 or higher.

References

• GitHub Commit
• GitHub Commit
• NPM Security Advisory

Overview

qs is a querystring parser that supports nesting and arrays, with a depth limit.

Affected versions of this package are vulnerable to Denial of Service (DoS). When parsing a string representing a deeply nested object, qs will block the event loop for long periods of time. Such a delay may hold up the server's resources, keeping it from processing other requests in the meantime, thus enabling a Denial-of-Service attack.

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:

1. CCC
2. CC+C
3. C+CC
4. 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.

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 qs to version 1.0.0 or higher.

References

• Node Security Advisory

Overview

Affected versions of this package are vulnerable to Cross-site Scripting (XSS) via the cookie name, path, or domain, which can be used to set unexpected values to other cookie fields.

Workaround

Users who are not able to upgrade to the fixed version should avoid passing untrusted or arbitrary values for the cookie fields and ensure they are set by the application instead of 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 &lt; and > can be coded as &gt; 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:

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 cookie to version 0.7.0 or higher.

References

• GitHub Commit
• GitHub PR
• Red Hat Bugzilla Bug

Overview

connect is a stack of middleware that is executed in order in each request.

Affected versions of this package are vulnerable to Cross-site Scripting (XSS). The "methodOverride" middleware allows the HTTP post to override the method of the request with the value of the _method post key or with the header x-http-method-override.

Due to improper user input sanitization, the req.method could contain any kind of value. Because the req.method did not match any common method VERB, connect answered with a 404 page containing the "Cannot [method] [url]" content. The method was not properly encoded for output in the browser.

PoC

curl "localhost:3000" -d "_method=<script src=http://nodesecurity.io/xss.js></script>"
Cannot <SCRIPT SRC=HTTP://NODESECURITY.IO/XSS.JS></SCRIPT> /

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 &lt; and > can be coded as &gt; 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:

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 connect to version 2.8.2 or higher.

References

• GitHub Commit
• GitHub Commit
• GitHub Issue
• X-force Vulnerability Report

Overview

ejs is a popular JavaScript templating engine. Affected versions of the package are vulnerable to Cross-site Scripting by letting the attacker under certain conditions control and override the filename option causing it to render the value as is, without escaping it. You can read more about this vulnerability on the Snyk blog.

There's also a Remote Code Execution & Denial of Service vulnerabilities caused by the same behaviour.

Details

ejs provides a few different options for you to render a template, two being very similar: ejs.render() and ejs.renderFile(). The only difference being that render expects a string to be used for the template and renderFile expects a path to a template file.

Both functions can be invoked in two ways. The first is calling them with template, data, and options:

ejs.render(str, data, options);

ejs.renderFile(filename, data, options, callback)

The second way would be by calling only the template and data, while ejs lets the options be passed as part of the data:

ejs.render(str, dataAndOptions);

ejs.renderFile(filename, dataAndOptions, callback)

If used with a variable list supplied by the user (e.g. by reading it from the URI with qs or equivalent), an attacker can control ejs options. This includes the filename option, which will be rendered as is when an error occurs during rendering.

ejs.renderFile('my-template', {filename:'<script>alert(1)</script>'}, callback);

The fix introduced in version 2.5.3 blacklisted root options from options passed via the data object.

Disclosure Timeline

• November 28th, 2016 - Reported the issue to package owner.
• November 28th, 2016 - Issue acknowledged by package owner.
• December 06th, 2016 - Issue fixed and version 2.5.5 released.

Remediation

The vulnerability can be resolved by either using the GitHub integration to generate a pull-request from your dashboard or by running snyk wizard from the command-line interface. Otherwise, Upgrade ejs to version 2.5.5 or higher.

References

• Snyk Blog
• Fix commit

Overview

ejs is a popular JavaScript templating engine. Affected versions of the package are vulnerable to Denial of Service by letting the attacker under certain conditions control and override the localNames option causing it to crash. You can read more about this vulnerability on the Snyk blog.

There's also a Remote Code Execution & Cross-site Scripting vulnerabilities caused by the same behaviour.

Details

ejs provides a few different options for you to render a template, two being very similar: ejs.render() and ejs.renderFile(). The only difference being that render expects a string to be used for the template and renderFile expects a path to a template file.

Both functions can be invoked in two ways. The first is calling them with template, data, and options:

ejs.render(str, data, options);

ejs.renderFile(filename, data, options, callback)

The second way would be by calling only the template and data, while ejs lets the options be passed as part of the data:

ejs.render(str, dataAndOptions);

ejs.renderFile(filename, dataAndOptions, callback)

If used with a variable list supplied by the user (e.g. by reading it from the URI with qs or equivalent), an attacker can control ejs options. This includes the localNames option, which will cause the renderer to crash.

ejs.renderFile('my-template', {localNames:'try'}, callback);

The fix introduced in version 2.5.3 blacklisted root options from options passed via the data object.

Disclosure Timeline

• November 28th, 2016 - Reported the issue to package owner.
• November 28th, 2016 - Issue acknowledged by package owner.
• December 06th, 2016 - Issue fixed and version 2.5.5 released.

Remediation

The vulnerability can be resolved by either using the GitHub integration to generate a pull-request from your dashboard or by running snyk wizard from the command-line interface. Otherwise, Upgrade ejs to version 2.5.5 or higher.

References

• Snyk Blog
• Fix commit

Overview

ejs is a popular JavaScript templating engine.

Affected versions of this package are vulnerable to Improper Control of Dynamically-Managed Code Resources due to the lack of certain pollution protection mechanisms. An attacker can exploit this vulnerability to manipulate object properties that should not be accessible or modifiable.

Note:

Even after updating to the fix version that adds enhanced protection against prototype pollution, it is still possible to override the hasOwnProperty method.

Remediation

Upgrade ejs to version 3.1.10 or higher.

References

• GitHub Commit
• PoC

Overview

Send is a library for streaming files from the file system as an http response. It supports partial responses (Ranges), conditional-GET negotiation, high test coverage, and granular events which may be leveraged to take appropriate actions in your application or framework.

Affected versions of this package are vulnerable to a Root Path Disclosure.

Remediation

Upgrade send to version 0.11.1 or higher. If a direct dependency update is not possible, use snyk wizard to patch this vulnerability.

References

• GitHub PR
• GitHub Commit
• GitHub History
• Expressjs Security Update

Overview

send is a library for streaming files from the file system.

Affected versions of this package are vulnerable to Directory-Traversal attacks due to insecure comparison. When relying on the root option to restrict file access a malicious user may escape out of the restricted directory and access files in a similarly named directory. For example, a path like /my-secret is consedered fine for the root /my.

Details

A Directory Traversal attack (also known as path traversal) aims to access files and directories that are stored outside the intended folder. By manipulating files with "dot-dot-slash (../)" sequences and its variations, or by using absolute file paths, it may be possible to access arbitrary files and directories stored on file system, including application source code, configuration, and other critical system files.

Directory Traversal vulnerabilities can be generally divided into two types:

• Information Disclosure: Allows the attacker to gain information about the folder structure or read the contents of sensitive files on the system.

st is a module for serving static files on web pages, and contains a vulnerability of this type. In our example, we will serve files from the public route.

If an attacker requests the following URL from our server, it will in turn leak the sensitive private key of the root user.

curl http://localhost:8080/public/%2e%2e/%2e%2e/%2e%2e/%2e%2e/%2e%2e/root/.ssh/id_rsa

Note %2e is the URL encoded version of . (dot).

• Writing arbitrary files: Allows the attacker to create or replace existing files. This type of vulnerability is also known as Zip-Slip.

One way to achieve this is by using a malicious zip archive that holds path traversal filenames. When each filename in the zip archive gets concatenated to the target extraction folder, without validation, the final path ends up outside of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicious file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:

2018-04-15 22:04:29 .....           19           19  good.txt
2018-04-15 22:04:42 .....           20           20  ../../../../../../root/.ssh/authorized_keys

Remediation

Upgrade to a version greater than or equal to 0.8.4.

References

• GitHub PR
• GitHub Commit

Overview

ejs is a popular JavaScript templating engine.

Affected versions of this package are vulnerable to Arbitrary Code Injection via the render and renderFile. If external input is flowing into the options parameter, an attacker is able run arbitrary code. This include the filename, compileDebug, and client option.

POC

let ejs = require('ejs')
ejs.render('./views/test.ejs',{
    filename:'/etc/passwd\nfinally { this.global.process.mainModule.require(\'child_process\').execSync(\'touch EJS_HACKED\') }',
    compileDebug: true,
    message: 'test',
    client: true
})

Remediation

Upgrade ejs to version 3.1.6 or higher.

References

• GitHub Commit
• GitHub Issue