Unsafe Object Deserialization

Affecting angular package, versions >=1.2.19 <1.2.24

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Overview

angular is a package that lets you write client-side web applications as if you had a smarter browser. It also lets you use HTML as your template language and lets you extend HTML’s syntax to express your application’s components clearly and succinctly.

Affected versions of this package are vulnerable to Unsafe Object Deserialization.

POC

The exploitable code:

hasOwnProperty.constructor.prototype.valueOf = valueOf.call;
    ["a", "alert(1)"].sort(hasOwnProperty.constructor);

The exploit:

    1. Array.sort takes a comparison function and passes it 2 parameters to compare.
    2. It then calls .valueOf() if the result is not a primitive.
  • The Function object conveniently accepts two string arguments so so it can be used to construct a function. However, this doesn't do much unless it can be executed.
  • The valueOf function on Function.prototype was set to Function.prototype.call. This causes the function constructed to be executed when sort calls .valueOf() on the result of the comparison.

Details

Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating object from sequence of bytes is called deserialization. Serialization is commonly used for communication (sharing objects between multiple hosts) and persistence (store the object state in a file or a database). It is an integral part of popular protocols like Remote Method Invocation (RMI), Java Management Extension (JMX), Java Messaging System (JMS), Action Message Format (AMF), Java Server Faces (JSF) ViewState, etc.

Deserialization of untrusted data (CWE-502), is when the application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, letting the attacker to control the state or the flow of the execution.

Java deserialization issues have been known for years. However, interest in the issue intensified greatly in 2015, when classes that could be abused to achieve remote code execution were found in a popular library (Apache Commons Collection). These classes were used in zero-days affecting IBM WebSphere, Oracle WebLogic and many other products.

An attacker just needs to identify a piece of software that has both a vulnerable class on its path, and performs deserialization on untrusted data. Then all they need to do is send the payload into the deserializer, getting the command executed.

Developers put too much trust in Java Object Serialization. Some even de-serialize objects pre-authentication. When deserializing an Object in Java you typically cast it to an expected type, and therefore Java's strict type system will ensure you only get valid object trees. Unfortunately, by the time the type checking happens, platform code has already created and executed significant logic. So, before the final type is checked a lot of code is executed from the readObject() methods of various objects, all of which is out of the developer's control. By combining the readObject() methods of various classes which are available on the classpath of the vulnerable application an attacker can execute functions (including calling Runtime.exec() to execute local OS commands).

  • Apache Blog

Remediation

Upgrade angular to version 1.2.24 or higher.

References

CVSS Score

7.4
high severity
  • Attack Vector
    Network
  • Attack Complexity
    High
  • Privileges Required
    None
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    High
  • Integrity
    High
  • Availability
    None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Credit
Chirayu Krishnappa
CWE
CWE-502
Snyk ID
npm:angular:20140909
Disclosed
08 Sep, 2014
Published
23 Jan, 2017