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

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-14 · updated 2026-07-16
Weakness: CWE-93

Description

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.

Affected products

symfony: before 5.4.52; from 6.0.0 before 6.4.40; from 7.0.0 before 7.4.12; from 8.0.0 before 8.0.12 — fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12
Packagist Symfony/Mime: before 5.4.52; from 6.0.0 before 6.4.40; from 7.0.0 before 7.4.12; from 8.0.0 before 8.0.12; v4.3.0, v4.3.0-BETA1, v4.3.0-BETA2, v4.3.0-RC1, v4.3.1, v4.3.10 (+253) — fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12
Packagist Symfony/Symfony: before 5.4.52; from 6.0.0 before 6.4.40; from 7.0.0 before 7.4.12; from 8.0.0 before 8.0.12; 2.0.4, 2.0.5, 2.0.6, 2.0.7, v2.0.10, v2.0.11 (+696) — fixed in 5.4.52, 6.4.40, 7.4.12, 8.0.12

How to fix

Upgrade to a fixed version: symfony 5.4.52, 6.4.40, 7.4.12, 8.0.12; Packagist Symfony/Mime 5.4.52, 6.4.40, 7.4.12, 8.0.12; Packagist Symfony/Symfony 5.4.52, 6.4.40, 7.4.12, 8.0.12. Check the vendor advisory for mitigations.

References

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