c-ares up to 1.34.4 read_answers use after free

Summaryinfo

A vulnerability, which was classified as critical, has been found in c-ares up to 1.34.4. This issue affects the function read_answers. The manipulation leads to use after free. This vulnerability is uniquely identified as CVE-2025-31498. The attack is possible to be carried out remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in c-ares up to 1.34.4. It has been rated as critical. This issue affects the function read_answers. The manipulation with an unknown input leads to a use after free vulnerability. Using CWE to declare the problem leads to CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

c-ares is an asynchronous resolver library. From 1.32.3 through 1.34.4, there is a use-after-free in read_answers() when process_answer() may re-enqueue a query either due to a DNS Cookie Failure or when the upstream server does not properly support EDNS, or possibly on TCP queries if the remote closed the connection immediately after a response. If there was an issue trying to put that new transaction on the wire, it would close the connection handle, but read_answers() was still expecting the connection handle to be available to possibly dequeue other responses. In theory a remote attacker might be able to trigger this by flooding the target with ICMP UNREACHABLE packets if they also control the upstream nameserver and can return a result with one of those conditions, this has been untested. Otherwise only a local attacker might be able to change system behavior to make send()/write() return a failure condition. This vulnerability is fixed in 1.34.5.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2025-31498 since 03/28/2025. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

The vulnerability scanner Nessus provides a plugin with the ID 234193 (Linux Distros Unpatched Vulnerability : CVE-2025-31498), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 1.34.5 eliminates this vulnerability. Applying the patch 29d38719112639d8c0ba910254a3dd4f482ea2d1 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (234193) and CERT Bund (WID-SEC-2025-1850). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Xerox FreeFlow Print Server

Productinfo

Name

• c-ares

Version

• 1.34.0
• 1.34.1
• 1.34.2
• 1.34.3
• 1.34.4

License

• open-source

Website

• Product: https://github.com/c-ares/c-ares/

CPE 2.3info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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