CVE-2025-9901: Libsoup2.4 · A flaw was found in libsoup’s caching mechanism, SoupCache, where the HTTP Vary header is
Affects libsoup2.4Source GCVE Database
Not known to be exploited · CVSS 5.9 Medium.
Data as of 3 Nov 2026, 23:13 UTC
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 3 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 3 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10libsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10libsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlibsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu Pro 26.04 LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-apps/resoluteOther threats | Affected
| Fixed in– |
Ubuntu 25.10libsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10libsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=questingOther threats | Affected
| Fixed in– |
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Description
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.