Unauthorized sign-up via ambiguous email addresses
Published Apr 23, 2026 · Updated Apr 23, 2026
Email validation in affected Mastodon releases before 4.3.22, 4.4.16, or 4.5.9 allows remote attackers to bypass sign-up domain controls. EmailAddressValidator accepted percent signs, commas, and quotes, allowing the domain restriction check to approve an address that a mail server resolves differently. No existing account or user interaction is required, but exploitation requires open registration and an email domain block or allow-list; the result is unauthorized account creation.
Summary
What happened
Email validation in affected Mastodon releases before 4.3.22, 4.4.16, or 4.5.9 allows remote attackers to bypass sign-up domain controls. EmailAddressValidator accepted percent signs, commas, and quotes, allowing the domain restriction check to approve an address that a mail server resolves differently. No existing account or user interaction is required, but exploitation requires open registration and an email domain block or allow-list; the result is unauthorized account creation.
The record
- CVE
- CVE-2026-41259
- Published
- Apr 23, 2026
- Updated
- Apr 23, 2026
- Vendor
- Mastodon
- Product
- Mastodon
- Classifications
- CWE-841
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 23, 2026CVE publishedPublication date reported by the CVE source.
- Apr 23, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 4.3.22
- Affected versionversion=>= 4.4.0-beta.1, < 4.4.16
- Affected versionversion=>= 4.5.0-beta.1, < 4.5.9
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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