CVE-2026-23962
Published: 22 January 2026
Summary
CVE-2026-23962 is a high-severity Allocation of Resources Without Limits or Throttling (CWE-770) vulnerability in Joinmastodon Mastodon. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 17.6th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SC-5 (Denial-of-service Protection) and SC-6 (Resource Availability).
Deeper analysis
CVE-2026-23962 is a resource exhaustion vulnerability in Mastodon, a free, open-source social network server based on ActivityPub. Affected versions are those prior to v4.3.18, v4.4.12, and v4.5.5, where there is no limit on the maximum number of poll options in remote posts. This allows attackers to create polls with an excessively large number of options, leading to greatly increased resource consumption and potential denial-of-service (DoS) conditions. The vulnerability is rated with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and is associated with CWE-770 (Allocation of Resources Without Limits or Throttling).
Any unauthenticated attacker with network access can exploit this vulnerability by posting remote content containing a poll with a very large number of options. The disproportionate resource usage impacts both Mastodon servers and clients, depending on the scale of options included, resulting in server-side or client-side DoS.
Mitigation is available through patches released in Mastodon versions v4.3.18, v4.4.12, and v4.5.5, as detailed in the corresponding GitHub release notes and the security advisory GHSA-gg8q-rcg7-p79g. Administrators should upgrade to one of these fixed versions to prevent exploitation.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-4208
Vulnerability details
Mastodon is a free, open-source social network server based on ActivityPub. Mastodon versions before v4.3.18, v4.4.12, and v4.5.5 do not have a limit on the maximum number of poll options for remote posts, allowing attackers to create polls with a…
more
very large amount of options, greatly increasing resource consumption. Depending on the number of poll options, an attacker can cause disproportionate resource usage in both Mastodon servers and clients, potentially causing Denial of Service either server-side or client-side. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Direct exploitation of public-facing Mastodon server via remote ActivityPub content to trigger application resource exhaustion DoS.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
SC-5 Denial-of-service Protection directly mitigates resource exhaustion by requiring limits on resource usage for incoming requests like polls with excessive options.
SC-6 Resource Availability enforces limits on resource allocation to prevent disproportionate consumption from processing large numbers of poll options.
SI-10 Information Input Validation checks the format and quantity of poll options in remote ActivityPub posts to reject those exceeding safe limits before processing.