CVE-2026-23962 Mastodon vulnerable to Denial of Service from a single post (client/server)
Attackers can cause Denial of Service on Mastodon servers and clients by creating posts with excessive poll options, requiring an upgrade to patched versions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23962?
CVE-2026-23962 is a high-severity denial of service vulnerability in mastodon, published on 22 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-770
Which versions are affected by CVE-2026-23962?
1 open source package ship an affected version, including mastodon. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
mastodon Bitnami | All versions | 4.3.18, 4.4.12, 4.5.5 |
Products include Joinmastodon Mastodon.
How do I fix CVE-2026-23962?
Upgrade mastodon to a fixed version for your release line: 4.3.18, 4.4.12 or 4.5.5.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-23962 being exploited?
There is no known exploitation of CVE-2026-23962 in the wild and no public exploit code.
Other vulnerabilities in mastodon
- CVE-2023-36460 Mastodon vulnerable to arbitrary file creation through media attachments
- CVE-2022-2166 Improper Restriction of Excessive Authentication Attempts in mastodon/mastodon
- CVE-2022-24307 Missing authorization in n/a
- CVE-2018-21018 Auth bypass in n/a
- CVE-2024-23832 Mastodon Remote user impersonation and takeover
Sources
Also known as BIT-mastodon-2026-23962, GHSA-gg8q-rcg7-p79g.