Improper Enforcement of Behavioral Workflow in Mastodon - CVE-2026-41259
Published: April 23, 2026
Vulnerability identifier: #VU126999
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-41259
CWE-ID: CWE-841
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass e-mail domain restrictions for signing up.
The vulnerability exists due to improper enforcement of behavioral workflow in e-mail address validation when processing sign-up requests. A remote attacker can use special characters in an e-mail address to bypass e-mail domain restrictions for signing up.
The issue can affect both blocked domains and allow-listed domains because some mail servers interpret certain characters differently.
Affected software
Mastodon
How to mitigate CVE-2026-41259
Install security update from vendor's website.
Mastodon - addressed in versions 4.3.22, 4.4.16, 4.5.9