How severe is CVE-2026-45070?

No CVSS score has been assigned to CVE-2026-45070 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-45070?

CVE-2026-45070 affects the following packages: symfony/mime (Packagist), symfony/symfony (Packagist), symfony/mime (Packagist), symfony/mime (Packagist), symfony/mime (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-45070?

Update symfony/mime to 5.4.52 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45070 is resolved across your whole dependency graph.

How do I detect CVE-2026-45070 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/mime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-45070 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-45070 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-45070 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-45070?

CVE-2026-45070 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 31th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-45070?

CVE-2026-45070 is classified as CWE-93 (CWE-93). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-45070 published, and has it been updated?

CVE-2026-45070 was published on July 14, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-45070 — mime

Fix: symfony/symfony@e62ea21

CVE-2026-45070 is a CWE-93 vulnerability in symfony/mime. A fix is available for symfony/mime — see the affected versions and patch details below.

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

Also known asGHSA-vqc8-7275-q272

Published

Jul 14, 2026

Updated

Aug 12, 2026

Affected

8 pkgs

Patched

8 / 8

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-45070.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs31th percentile — riskier than 31% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

8 pkgs affected

🐘symfony/mime🐘symfony/symfony🐘symfony/mime🐘symfony/mime🐘symfony/mime🐘symfony/symfony🐘symfony/symfony🐘symfony/symfony

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

8 total 8 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/mime`	all versions	5.4.52`composer require symfony/mime:^5.4.52`
🐘Packagist	`symfony/symfony`	all versions	5.4.52`composer require symfony/symfony:^5.4.52`
🐘Packagist	`symfony/mime`	≥ 6.0.0&&< 6.4.40	6.4.40`composer require symfony/mime:^6.4.40`
🐘Packagist	`symfony/mime`	≥ 7.0.0&&< 7.4.12	7.4.12`composer require symfony/mime:^7.4.12`
🐘Packagist	`symfony/mime`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/mime:^8.0.12`
🐘Packagist	`symfony/symfony`	≥ 6.0.0&&< 6.4.40	6.4.40`composer require symfony/symfony:^6.4.40`

Affected Products

1 product · 4 configurations

Application

symfonysensiolabs

≥ 8.0.0 && < 8.0.12

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/mime, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/mime to 5.4.52 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45070 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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