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TI-2026-21875 Aliases CVE-2026-27468

Mastodon may allow unconfirmed FASP to make subscriptions

Priority LOW 22CWE-862Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
Security bypass
Confidentiality · integrity · availability
Low · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-862.

Summary

Mastodon is a free, open-source social network server based on ActivityPub. FASP registration requires manual approval by an administrator. In versions 4.4.0 through 4.4.13 and 4.5.0 through 4.5.6, actions performed by a FASP to subscribe to account/content lifecycle events or to backfill content did not check properly whether the FASP was actually approved. This only affects Mastodon servers that have opted in to testing the experimental FASP feature by setting the environment variable `EXPERIMENTAL_FEATURES` to a value including `fasp`. An attacker can make subscriptions and request content backfill without approval by an administrator. Done once, this leads to minor information leak of URIs that are publicly available anyway. But done several times this is a serious vector for DOS, putting pressure on the sidekiq worker responsible for the `fasp` queue. The fix is included in the 4.4.14 and 4.5.7 releases. Admins that are actively testing the experimental "fasp" feature should update their systems. Servers not using the experimental feature flag `fasp` are not affected.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00299 22nd percentileScored 2026-11-07
Fix Fixed mastodon (mastodon): 4.4.14, 4.5.7

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
mastodonmastodon4.4.0 to before 4.4.14; 4.5.0 to before 4.5.74.4.14, 4.5.7Patch availableCNA
  • mastodon Vendormastodon Affected 4.4.0 to before 4.4.14; 4.5.0 to before 4.5.7 Fixed in 4.4.14, 4.5.7 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*4.4.0 to before 4.4.14; 4.5.0 to before 4.5.7Vulnerablemastodon
  • cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* Versions 4.4.0 to before 4.4.14; 4.5.0 to before 4.5.7 Vulnerable ·mastodon

Remediation

  • Fix · CNA mastodon (mastodon) Fixed in 4.4.14, 4.5.7

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-27468

References

Patch 2

  • TI-2022-02004 Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon CVSS 3.1CRITICAL 9.8
  • TI-2025-34613 Mastodon e‑mail throttle misconfiguration allows unlimited email confirmations against unconfirmed emails CVSS 3.1HIGH 7.5
  • TI-2022-22936 Mastodon through 4.0.2 allows attackers to cause a denial of service (large Sidekiq pull… CVSS 3.1HIGH 7.5
  • TI-2023-18301 Mastodon vulnerable to arbitrary file creation through media attachments CVSS 3.1CRITICAL 10.0
  • TI-2023-13359 Mastodon's blind LDAP injection in login allows the attacker to leak arbitrary attributes from LDAP database CVSS 3.1HIGH 7.7
  • TI-2024-16846 External OpenID Connect Account Takeover by E-Mail Change in mastodon CVSS 3.1HIGH 7.4
See all 41 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences