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CVE-2026-25540
Good to know:
Date: February 4, 2026
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.
Severity Score
Severity Score
Weakness Type (CWE)
Use of Cache Containing Sensitive Information
CWE-524Top Fix
Upgrade Version
Upgrade to version https://github.com/mastodon/mastodon.git - v4.5.6;https://github.com/mastodon/mastodon.git - v4.4.13;https://github.com/mastodon/mastodon.git - v4.3.19
CVSS v3.1
| Base Score: |
|
|---|---|
| Attack Vector (AV): | NETWORK |
| Attack Complexity (AC): | LOW |
| Privileges Required (PR): | NONE |
| User Interaction (UI): | NONE |
| Scope (S): | UNCHANGED |
| Confidentiality (C): | LOW |
| Integrity (I): | NONE |
| Availability (A): | LOW |