Read the docs
TI-2026-19305 Aliases CVE-2026-23963

Mastodon missing length limits on list names, filter names, and filter keywords

Priority LOW 29CWE-770Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA. Impact type from CWE-770.

Summary

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, the server does not enforce a maximum length for the names of lists or filters, or for filter keywords, allowing any user to set an arbitrarily long string as the name or keyword. Any local user can abuse the list or filter fields to cause disproportionate storage and computing resource usage. They can additionally cause their own web interface to be unusable, although they must intentionally do this to themselves or unknowingly approve a malicious API client. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00352 29th percentileScored 2026-11-07
Fix Fixed mastodon (mastodon): 4.3.18, 4.4.12, 4.5.5

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
mastodonmastodonbefore 4.3.18; 4.4.0 to before 4.4.12; 4.5.0 to before 4.5.54.3.18, 4.4.12, 4.5.5Patch availableCNA
  • mastodon Vendormastodon Affected before 4.3.18; 4.4.0 to before 4.4.12; 4.5.0 to before 4.5.5 Fixed in 4.3.18, 4.4.12, 4.5.5 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:*before 4.3.18; 4.4.0 to before 4.4.12; 4.5.0 to before 4.5.5Vulnerablemastodon
  • cpe:2.3:a:joinmastodon:mastodon:*:*:*:*:*:*:*:* Versions before 4.3.18; 4.4.0 to before 4.4.12; 4.5.0 to before 4.5.5 Vulnerable ·mastodon

Remediation

  • Fix · CNA mastodon (mastodon) Fixed in 4.3.18, 4.4.12, 4.5.5

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-23963

References

Advisory 1

Other 3

  • 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