CVE-2026-45070: Symfony: Email Header Injection via Non-Token Characters in Mime Parameter Names

Published May 27, 2026
·
Updated

Description

Symfony\Component\Mime\Header\ParameterizedHeader (and the related parameter handling reachable from Symfony\Component\Mime\Header\Headers) is responsible for serializing structured headers such as Content-Type and Content-Disposition, which carry key=value parameters (e.g. Content-Disposition: attachment; filename="x").

RFC 2045 / RFC 5322 require parameter names to be tokens: a restricted ASCII subset that excludes whitespace, CR/LF, and the tspecials set. Symfony's parameter handling validates and properly encodes parameter values, but does not validate parameter names: the supplied name is emitted verbatim into the serialized header.

A caller that derives a parameter name from untrusted input, e.g. an application that lets a user influence a Content-Disposition parameter name, can include \r\n or other non-token bytes inside the name, terminating the current header and injecting additional headers in the rendered message. This is the classic CRLF / header-injection primitive applied to the parameter-name slot.

Resolution

ParameterizedHeader now rejects parameter names that contain bytes outside the RFC token character class.

The patch for this issue is available here for branch 5.4.

Credits

Symfony would like to thank Fabian Fleischer for reporting the issue and Alexandre Daubois for fixing it.

Other sources

Symfony is a PHP framework for web and console applications and a set of reusable PHP components. Prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12, Symfony\Component\Mime\Header\ParameterizedHeader validates and encodes parameter values but emits parameter names verbatim, allowing a caller that derives a parameter name from untrusted input to include CRLF or other non-token bytes and inject additional headers into rendered structured mail headers such as Content-Type or Content-Disposition. This issue is reported as fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

— MITRE

Affected Software

12 affected componentsFixes available
composer/symfony/symfony>=8.0.0<8.0.12
8.0.12
composer/symfony/symfony>=7.0.0<7.4.12
7.4.12
composer/symfony/symfony>=6.0.0<6.4.40
6.4.40
composer/symfony/mime>=8.0.0<8.0.12
8.0.12
composer/symfony/mime>=7.0.0<7.4.12
7.4.12
composer/symfony/mime>=6.0.0<6.4.40
6.4.40
composer/symfony/symfony<5.4.52
5.4.52
composer/symfony/mime<5.4.52
5.4.52
SensioLabs Symfony<5.4.52
SensioLabs Symfony>=6.0.0<6.4.40
SensioLabs Symfony>=7.0.0<7.4.12
SensioLabs Symfony>=8.0.0<8.0.12

Remediation

Recommended actions to resolve this vulnerability, in priority order.

  1. Upgrade

    Upgrade composer/symfony/symfony to a version that resolves this vulnerability.

    Fixed in 8.0.12
  2. Upgrade

    Upgrade composer/symfony/symfony to a version that resolves this vulnerability.

    Fixed in 7.4.12
  3. Upgrade

    Upgrade composer/symfony/symfony to a version that resolves this vulnerability.

    Fixed in 6.4.40
  4. Upgrade

    Upgrade composer/symfony/mime to a version that resolves this vulnerability.

    Fixed in 8.0.12
  5. Upgrade

    Upgrade composer/symfony/mime to a version that resolves this vulnerability.

    Fixed in 7.4.12
  6. Upgrade

    Upgrade composer/symfony/mime to a version that resolves this vulnerability.

    Fixed in 6.4.40
  7. Upgrade

    Upgrade composer/symfony/symfony to a version that resolves this vulnerability.

    Fixed in 5.4.52
  8. Upgrade

    Upgrade composer/symfony/mime to a version that resolves this vulnerability.

    Fixed in 5.4.52
  9. Upgrade

    Upgrade Symfony to a version that resolves this vulnerability.

    Fixed in 5.4.52
  10. Upgrade

    Upgrade Symfony to a version that resolves this vulnerability.

    Fixed in 6.4.40
  11. Upgrade

    Upgrade Symfony to a version that resolves this vulnerability.

    Fixed in 7.4.12
  12. Upgrade

    Upgrade Symfony to a version that resolves this vulnerability.

    Fixed in 8.0.12
  13. Upgrade

    Upgrade to a fixed release to a version that resolves this vulnerability.

    Patch e62ea217f8b4ca8ae922ad0f949e0c4dc1f9b613

Event History

May 27, 2026
Advisory Published
via GitHub·09:09 PM
Data Sourced
via GitHub·09:09 PM
DescriptionWeaknessAffected Software
Jul 14, 2026
CVE Published
via MITRE·06:25 PM
Data Sourced
via MITRE·06:25 PM
DescriptionWeakness
Data Sourced
via NVD·07:17 PM
RemedyDescriptionSeverityWeaknessAffected Software
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Frequently Asked Questions

1

What is the severity of CVE-2026-45070?

CVE-2026-45070 has a risk rating of 56.

2

What is CVE-2026-45070 about?

CVE-2026-45070 concerns a CRLF injection vulnerability in the Symfony Mime component affecting header serialization.

3

How do I fix CVE-2026-45070?

To fix CVE-2026-45070, update your Symfony packages to the latest version where the vulnerability is addressed.

4

Which software versions are affected by CVE-2026-45070?

CVE-2026-45070 affects the Symfony Mime component in the composer/symfony/symfony and composer/symfony/mime packages.

5

What types of headers are impacted by CVE-2026-45070?

CVE-2026-45070 affects structured headers such as Content-Type and Content-Disposition that utilize key=value parameters.

Company

Resources

Contact

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