Symfony: Email Header / SMTP Command Injection via CRLF in Symfony\Component\Mime\Address

Summary

`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.

Timeline

1. Jul 14, 2026, 5:41 PM UTCCVE published
2. Jul 14, 2026, 6:15 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jul 14, 2026, 6:15 PM UTCRecord last updated

Affected versions

• symfony symfony

  fixed in 5.4.52; From 6.0.0-BETA1 · fixed in 6.4.40; From 7.0.0-BETA1 · fixed in 7.4.12; From 8.0.0-BETA1 · fixed in 8.0.12

• symfony/mimePackagist

  fixed in 5.4.52

• symfony/symfonyPackagist

  fixed in 5.4.52

• symfony/mimePackagist

  From 6.0.0 · fixed in 6.4.40

• symfony/mimePackagist

  From 7.0.0 · fixed in 7.4.12

• symfony/mimePackagist

  From 8.0.0 · fixed in 8.0.12

• symfony/symfonyPackagist

  From 6.0.0 · fixed in 6.4.40

• symfony/symfonyPackagist

  From 7.0.0 · fixed in 7.4.12

• symfony/symfonyPackagist

  From 8.0.0 · fixed in 8.0.12

References 7