CVE-2026-23961

Name: CVE-2026-23961
Creator: NVD / NIST
Published: 2026-01-22T02:15:52.78+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.3/10EPSS 0.40%

Last modified Jun 17, 2026

CVE-2026-23961 is a medium-severity vulnerability rated 5.3/10 on the CVSS scale. Mastodon is a free, open-source social network server based on ActivityPub. Mastodon allows server administrators to suspend remote users to prevent interactions. EPSS estimates a 0.40% chance of exploitation in the next 30 days.

Description

Mastodon is a free, open-source social network server based on ActivityPub. Mastodon allows server administrators to suspend remote users to prevent interactions. However, some logic errors allow already-known posts from such suspended users to appear in timelines if boosted. Furthermore, under certain circumstances, previously-unknown posts from suspended users can be processed. This issue allows old posts from suspended users to occasionally end up on timelines on all Mastodon versions. Additionally, on Mastodon versions from v4.5.0 to v4.5.4, v4.4.5 to v4.4.11, v4.3.13 to v4.3.17, and v4.2.26 to v4.2.29, remote suspended users can partially bypass the suspension to get new posts in. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

0.40%

32.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-863

Affected Software

Vendor	Product	Versions
Joinmastodon	Mastodon	< 4.3.18
Joinmastodon	Mastodon	>= 4.4.0, < 4.4.12
Joinmastodon	Mastodon	>= 4.5.0, < 4.5.5

References

https://github.com/mastodon/mastodon/releases/tag/v4.3.18Release Notes
https://github.com/mastodon/mastodon/releases/tag/v4.4.12Release Notes
https://github.com/mastodon/mastodon/releases/tag/v4.5.5Release Notes
https://github.com/mastodon/mastodon/security/advisories/GHSA-5h2f-wg8j-xqwpVendor Advisory

Timeline

Published: Jan 22, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-23961?

How severe is CVE-2026-23961?

CVE-2026-23961 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.40% probability of exploitation in the next 30 days.

How do I fix CVE-2026-23961?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-23961?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST