Skip to content
Log inStart free trial

GHSA-6w62-hx7r-mw68 CVE-2021-39154

XStream is vulnerable to an Arbitrary Code Execution attack

High Maven
Severity
8.5 / 10
High · CVSS 3.1
Exploit chance (EPSS)
4.74%
Chance of exploitation in the next 30 days. Higher than 91.86% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-434 Unrestricted Upload of File with Dangerous Type
CWE-502 Deserialization of Untrusted Data
Fix
1.4.18
Upgrade com.thoughtworks.xstream:xstream to this version or later

Description

Impact

The vulnerability may allow a remote attacker to load and execute arbitrary code from a remote host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.

Patches

XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

Workarounds

See workarounds for the different versions covering all CVEs.

References

See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for CVE-2021-39154.

Credits

ka1n4t found and reported the issue to XStream and provided the required information to reproduce it.

For more information

If you have any questions or comments about this advisory:

Affected versions

Maven

PackageVulnerableFixed in
com.thoughtworks.xstream:xstream
< 1.4.18
1.4.18

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

com.thoughtworks.xstream:xstream Maven → 1.4.18

maven
<dependency><groupId>com.thoughtworks.xstream</groupId><artifactId>xstream</artifactId><version>1.4.18</version></dependency>
gradle
implementation("com.thoughtworks.xstream:xstream:1.4.18")

Severity breakdown

CVSS 3.1 8.5

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack vector
Network
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Weakness

CWE-434: Unrestricted Upload of File with Dangerous Type

The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.

How to prevent it
  • Architecture and Design: Generate a new, unique filename for an uploaded file instead of using the user-supplied filename, so that no external input is used at all.[REF-422] [REF-423]
  • Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
  • Architecture and Design: Consider storing the uploaded files outside of the web document root entirely. Then, use other mechanisms to deliver the files dynamically. [REF-423]
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. For example, limiting filenames to alphanumeric characters can help to restrict the introduction of unintended file extensions.
  • Architecture and Design: Define a very limited set of allowable extensions and only generate filenames that end in these extensions. Consider the possibility of XSS (CWE-79) before allowing .html or .htm file types.
  • Implementation: Ensure that only one extension is used in the filename. Some web servers, including some versions of Apache, may process files based on inner extensions so that "filename.php.gif" is fed to the PHP interpreter.[REF-422] [REF-423]
  • Implementation: When running on a web server that supports case-insensitive filenames, perform case-insensitive evaluations of the extensions that are provided.
  • Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
  • Implementation: Do not rely exclusively on sanity checks of file contents to ensure that the file is of the expected type and size. It may be possible for an attacker to hide code in some file segments that will still be executed by the server. For example, GIF images may contain a free-form comments field.
  • Implementation: Do not rely exclusively on the MIME content type or filename attribute when determining how to render a file. Validating the MIME content type and ensuring that it matches the extension is only a partial solution.
  • Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
  • Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.

CWE-502: Deserialization of Untrusted Data

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

How to prevent it
  • Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
  • Implementation: When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
  • Implementation: Explicitly define a final object() to prevent deserialization.
  • Architecture and Design, Implementation: Make fields transient to protect them from deserialization. An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.
  • Implementation: Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.
  • Architecture and Design, Implementation: Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.
  • Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].

References

Advisories

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
CVE-2021-39144
XStream is vulnerable to a Remote Command Execution attack
High Known exploited Also affects com.thoughtworks.xstream:xstream
GHSA-hfq9-hggm-c56q
XStream is vulnerable to a Denial of Service attack due to stack overflow from a manipulated binary input stream
High Also affects com.thoughtworks.xstream:xstream
GHSA-f8cc-g7j8-xxpm
XStream can cause a Denial of Service by injecting deeply nested objects raising a stack overflow
High Also affects com.thoughtworks.xstream:xstream
GHSA-j563-grx4-pjpv
XStream can cause Denial of Service via stack overflow
High Also affects com.thoughtworks.xstream:xstream
GHSA-rmr5-cpv2-vgjf
Denial of Service by injecting highly recursive collections or maps in XStream
High Also affects com.thoughtworks.xstream:xstream
GHSA-64xx-cq4q-mf44
XStream is vulnerable to an Arbitrary Code Execution attack
High Also affects com.thoughtworks.xstream:xstream
GHSA-6wf9-jmg9-vxcc
XStream can cause a Denial of Service
Medium Also affects com.thoughtworks.xstream:xstream
GHSA-g5w6-mrj7-75h2
XStream is vulnerable to an Arbitrary Code Execution attack
High Also affects com.thoughtworks.xstream:xstream
Is this in your code?

MergeHarbor checks every repository's dependencies against this database, ranks what matters by exploitability and reachability, routes it to the owning team and opens the fix pull request.

Check your repos with MergeHarbor