CVE-2026-45067: Email Header / SMTP Command Injection via CRLF in Symfony\Component\Mime\Address
Description
Symfony\Component\Mime\Address is the value-object every Symfony Mailer address (to/cc/bcc/from/reply-to) flows through; its constructor is documented as validating the address and throwing on invalid input, so developers treat it as a security boundary.
The constructor accepts email addresses whose local-part (the part before @) is an RFC-5322 quoted string containing raw \r\n bytes — e.g. "x\r\nBcc: attacker@evil"@example.com. The stored address is later emitted verbatim into (1) the rendered message headers and (2) SmtpTransport's MAIL FROM:<...> / RCPT TO:<...> protocol lines, turning the embedded CRLF into a new mail header and/or a new SMTP command.
Resolution
The Address constructor now rejects addresses containing line breaks.
The patch for this issue is available here for branch 5.4.
Credits
We would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
Other sources
Description
Symfony\Component\Mime\Address is the value-object every Symfony Mailer address (to/cc/bcc/from/reply-to) flows through; its constructor is documented as validating the address and throwing on invalid input, so developers treat it as a security boundary.
The constructor accepts email addresses whose local-part (the part before @) is an RFC-5322 quoted string containing raw \r\n bytes, e.g. "x\r\nBcc: attacker@evil"@example.com. The stored address is later emitted verbatim into (1) the rendered message headers and (2) SmtpTransport's MAIL FROM:<...> / RCPT TO:<...> protocol lines, turning the embedded CRLF into a new mail header and/or a new SMTP command.
Resolution
The Address constructor now rejects addresses containing line breaks.
The patch for this issue is available here for branch 5.4.
Credits
We would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.
— GitHub
CVE-2026-45067: Email Header / SMTP Command Injection via CRLF in Symfony\Component\Mime\Address
— Packagist
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/mimeto a version that resolves this vulnerability.Fixed in 8.0.12 - Upgrade
Upgrade
composer/symfony/mimeto a version that resolves this vulnerability.Fixed in 7.4.12 - Upgrade
Upgrade
composer/symfony/mimeto a version that resolves this vulnerability.Fixed in 6.4.40 - Upgrade
Upgrade
composer/symfony/symfonyto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
composer/symfony/mimeto a version that resolves this vulnerability.Fixed in 5.4.52 - Upgrade
Upgrade
debian/symfonyto a version that resolves this vulnerability.Fixed in 5.4.53+dfsg-0+deb12u1Fixed in 6.4.41+dfsg-0+deb13u1Fixed in 6.4.49+dfsg-0+deb13u1Fixed in 7.4.22+dfsg-1Fixed in 7.4.23+dfsg-1 - Upgrade
Upgrade
symfony/symfonyto a version that resolves this vulnerability.Patch dc2dbd29211eb4ddc451373fa1374fb926e94604
Event History
Frequently Asked Questions
What is the severity of CVE-2026-45067?
The severity of CVE-2026-45067 is rated at 71, indicating a significant risk.
How do I fix CVE-2026-45067?
To fix CVE-2026-45067, update to the latest version of Symfony Mailer where the issue is addressed.
What kind of vulnerability is CVE-2026-45067?
CVE-2026-45067 is a CRLF Injection vulnerability related to the Symfony Mailer address validation.
Which software is affected by CVE-2026-45067?
CVE-2026-45067 affects the Symfony components, specifically composer/symfony/symfony and composer/symfony/mime.
What potential impact does CVE-2026-45067 have?
CVE-2026-45067 may allow an attacker to inject control characters into email headers, potentially leading to security breaches.