Is CVE-2026-23963 in the CISA KEV catalog?

No. CVE-2026-23963 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-23963?

CVE-2026-23963 has a CVSS v3 base score of 4.3 (MEDIUM).

What is the EPSS score for CVE-2026-23963?

CVE-2026-23963 has an EPSS score of 0.30% (21th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2026-23963?

Upgrade mastodon to 4.5.5 or later.

CVE & CISA-KEV Catalog

CVE-2026-23963

MEDIUM

4.3

CVSS v3

NVD

Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to versions 4.5.5, 4.4.12, and 4.3.18, the server does not enforce a maximum length for the names of lists or filters, or for filter keywords, allowing any user to set an arbitrarily long string as the name or keyword. Any local user can abuse the list or filter fields to cause disproportionate storage and computing resource usage. They can additionally cause their own web interface to be unusable, although they must intentionally do this to themselves or unknowingly approve a malicious API client. Mastodon versions v4.5.5, v4.4.12, v4.3.18 are patched.

CWE-770Allocation of Resources Without Limits or Throttling

How to fix

Remediation Available

mastodonNVD

Affected:>= 4.5.0, < 4.5.5Fixed in:4.5.5CVE-2026-23963derived 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 RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

0.30%probability of exploitation in 30 days

21stpercentile

Low risk: more likely to be exploited than 21% of all known CVEs.

References

Vendor Advisory1

github.com

Release Notes3

Related Vulnerabilities

Other CWE-770 (Allocation of Resources Without Limits or Throttling) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-50387	High	7.5	100%	-	Fix
CVE-2019-11478	Medium	5.3	95%	-	Fix
CVE-2019-11479	High	7.5	92%	-	Fix
CVE-2024-27316	High	7.5	91%	-	Fix
CVE-2022-30522	High	7.5	90%	-	Fix
CVE-2019-9515	High	7.5	88%	-	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.