libsoup HTTP Header Vary cache containing sensitive information

Summaryinfo

A vulnerability was found in libsoup. It has been classified as problematic. This affects an unknown part of the component HTTP Header Handler. The manipulation of the argument Vary leads to an unknown weakness. This vulnerability is listed as CVE-2025-9901. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in libsoup (unknown version) and classified as problematic. This issue affects an unknown code block of the component HTTP Header Handler. The manipulation of the argument Vary with an unknown input leads to a unknown weakness. Using CWE to declare the problem leads to CWE-524. The code uses a cache that contains sensitive information, but the cache can be read by an actor outside of the intended control sphere. Impacted is integrity. The summary by CVE is:

A flaw was found in libsoup’s caching mechanism, SoupCache, where the HTTP Vary header is ignored when evaluating cached responses. This header ensures that responses vary appropriately based on request headers such as language or authentication. Without this check, cached content can be incorrectly reused across different requests, potentially exposing sensitive user information. While the issue is unlikely to affect everyday desktop use, it could result in confidentiality breaches in proxy or multi-user environments.

The advisory is shared at bugzilla.redhat.com. The identification of this vulnerability is CVE-2025-9901. 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 price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/06/2025). MITRE ATT&CK project uses the attack technique T1592 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 261466 (Linux Distros Unpatched Vulnerability : CVE-2025-9901), which helps to determine the existence of the flaw in a target environment.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the databases at Tenable (261466) and EUVD (EUVD-2025-26502). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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Name

• libsoup

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• 🔒

CPE 2.2info

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

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