Use of cache containing sensitive information in Mastodon - CVE-2026-25540
Published: April 23, 2026
Vulnerability identifier: #VU126994
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-25540
CWE-ID: CWE-524
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Mastodon
Affected software:
Mastodon
Mastodon
Detailed vulnerability description
The vulnerability allows a remote attacker to disclose sensitive information and cause a denial of service.
The vulnerability exists due to use of a cache containing sensitive information in the ActivityPub endpoints for pinned posts and featured hashtags when handling signed HTTP requests with AUTHORIZED_FETCH enabled. A remote attacker can send crafted requests that manipulate cache state to disclose sensitive information and cause a denial of service.
This only occurs when AUTHORIZED_FETCH is enabled and the target user has blocked the actor or their server. Cached responses may be reused for up to 3 minutes across different signing actors.
How to mitigate CVE-2026-25540
Install security update from vendor's website.