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TI-2021-18099 Aliases CVE-2021-41267GHSA-q3j3-w37x-hq2q

Webcache Poisoning in Symfony

Priority LOW 31CWE-444Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
Required
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.

Summary

Symfony/Http-Kernel is the HTTP kernel component for Symfony, a PHP framework for web and console applications and a set of reusable PHP components. Headers that are not part of the "trusted_headers" allowed list are ignored and protect users from "Cache poisoning" attacks. In Symfony 5.2, maintainers added support for the `X-Forwarded-Prefix` headers, but this header was accessible in SubRequest, even if it was not part of the "trusted_headers" allowed list. An attacker could leverage this opportunity to forge requests containing a `X-Forwarded-Prefix` header, leading to a web cache poisoning issue. Versions 5.3.12 and later have a patch to ensure that the `X-Forwarded-Prefix` header is not forwarded to subrequests when it is not trusted.

Why it matters now

EPSS 0.0128 70th percentileScored 2026-11-07
Fix Fixed symfony (symfony): 5.3.12symfony/http-kernel (Packagist): 5.3.12+1 more product

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
symfonysymfony5.2.0 to before 5.3.125.3.12Patch availableCNA
—symfony/http-kernel (Packagist)5.2.0 to before 5.3.125.3.12Patch availableGHSA-q3j3-w37x-hq2q
—symfony/symfony (Packagist)5.2.0 to before 5.3.125.3.12Patch availableGHSA-q3j3-w37x-hq2q
  • symfony Vendorsymfony Affected 5.2.0 to before 5.3.12 Fixed in 5.3.12 Patch available CNA
  • symfony/http-kernel (Packagist) Vendor— Affected 5.2.0 to before 5.3.12 Fixed in 5.3.12 Patch available GHSA-q3j3-w37x-hq2q
  • symfony/symfony (Packagist) Vendor— Affected 5.2.0 to before 5.3.12 Fixed in 5.3.12 Patch available GHSA-q3j3-w37x-hq2q

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:*5.2.0 to before 5.3.12Vulnerablesensiolabs
  • cpe:2.3:a:sensiolabs:symfony:*:*:*:*:*:*:*:* Versions 5.2.0 to before 5.3.12 Vulnerable ·sensiolabs

Remediation

  • Fix · CNA symfony (symfony) Fixed in 5.3.12
  • Fix · GHSA-q3j3-w37x-hq2q symfony/http-kernel (Packagist) Fixed in 5.3.12 Advisory →
  • Fix · GHSA-q3j3-w37x-hq2q symfony/symfony (Packagist) Fixed in 5.3.12 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-41267
  2. 2026-10-03 Alias added: GHSA-q3j3-w37x-hq2q

References

Patch 3

Advisory 2

Other 3

  • TI-2024-33775 Ability to change environment from query in symfony/runtime CVSS 3.1HIGH 7.3
  • TI-2026-34283 Twig: The `spaceless` filter implicitly marks its output as safe CVSS 4.0MEDIUM 5.1
  • TI-2022-07667 Code injection in Twig CVSS 3.1CRITICAL 9.8
  • TI-2018-10028 Twig before 2.4.4 allows Server-Side Template Injection (SSTI) via the search search_key… CVSS 3.0CRITICAL 9.8
  • TI-2026-35851 Incorrect authorization in symfony CVSS 4.0HIGH 8.7
  • TI-2026-35264 Improper input validation in symfony CVSS 4.0HIGH 8.3
See all 94 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences