What is the CVSS score of CVE-2026-25540?

CVE-2026-25540 has a CVSS 3.1 base score of 6.5 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L. EPSS exploitation probability: 0.1%.

Which versions of Mastodon are affected by CVE-2026-25540?

Organizations using Mastodon should be aware of notable risk from CVE-2026-25540 rated CVSS 6.5. Exploitation could compromise the security of affected deployments.

How to fix or mitigate CVE-2026-25540?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

Mastodon CVE-2026-25540

MEDIUM

Use of Cache Containing Sensitive Information (CWE-524)

2026-02-04 security-advisories@github.com

Information Disclosure Mastodon

6.5

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

6.5 MEDIUM

AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

Low

Lifecycle Timeline

Analysis Generated

Mar 12, 2026 - 21:54 vuln.today

CVE Published

Feb 04, 2026 - 22:16 nvd

MEDIUM 6.5

DescriptionGitHub Advisory

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.3.19, 4.4.13, 4.5.6, Mastodon is vulnerable to web cache poisoning via `Rails.cache. When AUTHORIZED_FETCH is enabled, the ActivityPub endpoints for pinned posts and featured hashtags have contents that depend on the account that signed the HTTP request. However, these contents are stored in an internal cache and reused with no regards to the signing actor. As a result, an empty response generated for a blocked user account may be served to requests from legitimate non-blocked actors, or conversely, content intended for non-blocked actors may be returned to blocked actors. This issue has been patched in versions 4.3.19, 4.4.13, 4.5.6.

AnalysisAI

Mastodon versions prior to 4.3.19, 4.4.13, and 4.5.6 are vulnerable to web cache poisoning in ActivityPub endpoints when AUTHORIZED_FETCH is enabled, allowing cached responses to be served across different user contexts regardless of request signing. An attacker could exploit this to view content intended for non-blocked accounts or cause blocked users to receive empty responses meant for them, potentially bypassing access controls. No patch is currently available for affected deployments.

Technical ContextAI

Affects Mastodon. Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.3.19, 4.4.13, 4.5.6, Mastodon is vulnerable to web cache poisoning via `Rails.cache. When AUTHORIZED_FETCH is enabled, the ActivityPub endpoints for pinned posts and featured hashtags have contents that depend on the account that signed the HTTP request. However, these contents are stored in an internal cache and reused with no regards to the signing actor. As a result, an empty response generated for