Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization CRLF sequence sanitization
|
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Alert meAnalysisAIv1 – May 27, 2026
Header injection in Symfony's Mime component (symfony/mime) enables attackers to inject arbitrary MIME headers into serialized email messages when an application passes untrusted input as a parameter name to ParameterizedHeader. The component correctly encodes parameter values per RFC 2045/5322 but emits parameter names verbatim, meaning CRLF sequences in a user-influenced parameter name terminate the current header line and allow arbitrary new headers to be appended. No active exploitation is confirmed (not in CISA KEV), no public exploit code has been identified, and vendor-released patches are available across all supported Symfony branches.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 10 packages in composer, euvd
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
Primary rating from Vendor (https://github.com/symfony/symfony) · only source for this CVE.
CVSS VectorVendor: https://github.com/symfony/symfony
Lifecycle Timeline
1DescriptionCVE.org
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.
Threat Intelligence Overview
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.
EUVD-2026-44346
GHSA-vqc8-7275-q272
NVD
CVE.org
EPSS
Exploit-DB