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Vulnerabilities

Vulnerability · CVE-2026-25540

Mastodon is a free, open-source social network server based on ActivityPub.

Published Feb 4, 2026 · catalog updated Feb 5, 2026 · Mastodon is a free,

Last checked Nov 4, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-25540. EPSS is 0.44%. Act only if a listed version of Mastodon is a free, is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Mastodon is a free,).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
Medium6.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.44%
Remediation
Version ranges on file
Affected products
vendor mastodon mastodon < 4.3.19

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,

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor mastodon mastodon < 4.3.19< 4.3.19

How to fix CVE-2026-25540

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-25540. EPSS is 0.44%. Act only if a listed version of Mastodon is a free, is installed.

Which versions are affected?

Compare what you have installed with mastodon mastodon < 4.3.19 < 4.3.19. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.44%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Feb 4, 2026 · EUVD

    Detected

    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

  2. Feb 5, 2026 · EUVD

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-25540

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-25540

    30-day exploitation probability 0.44%

    first.org
  • EUVDVulnerability recordEUVD-2026-5329

    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

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 4, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 4, 2026
  • CVE.orgNov 4, 2026
  • EUVDNov 3, 2026