CVE-2026-41259

Q: How do I fix CVE-2026-41259?

Upgrade mastodon to 4.5.9 or later.

Q: Is CVE-2026-41259 being actively exploited?

Not that we know of. CVE-2026-41259 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.21% is the estimated probability that it will be exploited in the next 30 days. That is higher than 12% of all scored CVEs.

Q: How severe is CVE-2026-41259?

CVE-2026-41259 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-41259 affect?

Published advisories record a fix for mastodon (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

HIGH

7.5

CVSS v3

NVD

Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to v4.5.9, v4.4.16, and v4.3.22, Mastodon allows restricting new user sign-up based on e-mail domain names, and performs basic validation on e-mail addresses, but fails to restrict characters that are interpreted differently by some mailing servers. This vulnerability is fixed in v4.5.9, v4.4.16, and v4.3.22.

CWE-841

How to fix

Remediation Available

mastodonNVD

Affected:>= 4.5.0, < 4.5.9Fixed in:4.5.9CVE-2026-41259derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

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

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.21%probability of exploitation in 30 days

12thpercentile

Low risk: more likely to be exploited than 12% of all known CVEs.

References

Vendor Advisory1

github.com

Related Vulnerabilities

Other CWE-841 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2022-1667	High	7.5	1.2%	-	Fix
CVE-2023-4181	Medium	5.4	1.1%	-	-
CVE-2022-2105	Critical	9.4	1.0%	-	Fix
CVE-2022-2102	Critical	9.4	0.9%	-	Fix
CVE-2024-51738	High	8.1	0.6%	-	Fix
CVE-2024-37296	Medium	5.3	0.5%	-	-

Common questions

How do I fix CVE-2026-41259?

Upgrade mastodon to 4.5.9 or later.

Is CVE-2026-41259 being actively exploited?

Not that we know of. CVE-2026-41259 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.21% is the estimated probability that it will be exploited in the next 30 days. That is higher than 12% of all scored CVEs.

How severe is CVE-2026-41259?

CVE-2026-41259 has a CVSS v3 base score of 7.5, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-41259 affect?

Published advisories record a fix for mastodon (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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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 2026-04-28.