Mastodon
CVE-2026-23963
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V2 - Validation and Business Logic Resource allocation limits
MITRE ATT&CK
1 technique across 1 tactic: Impact The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS 4.3 (MEDIUM). Attack vector: Network. Complexity: Low. Privileges required: Low. User interaction: None. Exploitable via remote/network. |
| Exploit ScenarioDerived | A remote attacker could exploit this vulnerability to compromise the affected system. |
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Alert meAnalysisAIv1 – Mar 12, 2026
Mastodon prior to versions 4.5.5, 4.4.12, and 4.3.18 lacks input validation on list and filter names, allowing authenticated users to create arbitrarily long strings that consume excessive server resources and storage. A local attacker can exploit this to degrade system performance or render their own web interface unusable, though no patch is currently available for affected versions.
Earlier versions of this analysis (1)
Mastodon versions up to 4.5.5 is affected by allocation of resources without limits or throttling (CVSS 4.3).
RemediationAI
Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affects Mastodon. 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 mu
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Primary rating from GitHub Advisory · only source for this CVE.
CVSS VectorGitHub Advisory
DescriptionGitHub Advisory
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.
Executive ViewAI
Organizations using Mastodon should be aware of moderate risk from CVE-2026-23963 rated CVSS 4.3. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.
Apply vendor patch. If patching is delayed: restrict network access and enable monitoring.
Threat Intelligence Overview
NVD
CVE.org
EPSS
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)GitHub Advisory
Mastodon through 4.0.2 allows attackers to cause a denial of service (large Sidekiq pull queue) by creating bot accounts
Mastodon is a free, open-source social network server based on ActivityPub. Rated high severity (CVSS 7.4), this vulnera
Mastodon is a free, open-source social network server based on ActivityPub Mastodon allows configuration of LDAP for aut
Mastodon is a free, open-source social network server based on ActivityPub. Rated critical severity (CVSS 9.9), this vul
Mastodon is a free, open-source social network server based on ActivityPub Mastodon allows configuration of LDAP for aut
Improper Restriction of Excessive Authentication Attempts in GitHub repository mastodon/mastodon prior to 4.0.0. Rated c
Server-Side Request Forgery in Mastodon before 4.5.10, 4.4.17, and 4.3.23 lets attackers coerce the server into issuing
Server-side request forgery in Mastodon (versions before 4.5.10, 4.4.17, and 4.3.23) lets an attacker who controls autho
Mastodon prior to versions 4.5.8, 4.4.15, and 4.3.21 contains an unauthenticated Open Redirect vulnerability in the `/we
Unauthenticated attackers can bypass FASP administrator approval in Mastodon 4.4.0-4.4.13 and 4.5.0-4.5.6 to subscribe t
Sign-up restriction bypass in Mastodon (self-hosted ActivityPub social server) before v4.5.9, v4.4.16, and v4.3.22 allow
Mastodon is a self-hosted, federated microblogging platform. Rated high severity (CVSS 8.2), this vulnerability is remot
Exploit-DB