Is CVE-2026-23961 in the CISA KEV catalog?

No. CVE-2026-23961 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-23961?

CVE-2026-23961 has a CVSS v3 base score of 5.3 (MEDIUM).

What is the EPSS score for CVE-2026-23961?

CVE-2026-23961 has an EPSS score of 0.40% (32th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-23961?

Upgrade mastodon to 4.5.5 or later.

CVE & CISA-KEV Catalog

CVE-2026-23961

MEDIUM

5.3

CVSS v3

NVD

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.

CWE-863Incorrect Authorization

How to fix

Remediation Available

mastodonNVD

Affected:>= 4.5.0, < 4.5.5Fixed in:4.5.5CVE-2026-23961derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

0.40%probability of exploitation in 30 days

32ndpercentile

Low risk: more likely to be exploited than 32% of all known CVEs.

References

Vendor Advisory1

github.com

Release Notes3

Related Vulnerabilities

Other CWE-863 (Incorrect Authorization) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-22518	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2023-38035	Critical	9.8	100%	KEV + Ransom	-
CVE-2022-46169	Critical	9.8	100%	KEV	Fix
CVE-2025-29927	Critical	9.1	100%	-	Fix
CVE-2024-38856	Critical	9.8	99%	KEV	Fix
CVE-2020-36289	Medium	5.3	99%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-02-02.