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Fencer Intel
medium 6.5

CVE-2021-41267 json

Webcache Poisoning in Symfony

published 4y ago modified 4mo ago also BIT-symfony-2021-41267 , EUVD-2021-2377 , GHSA-q3j3-w37x-hq2q

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.3%
EPSS 1.3% chance of exploitation in 30 days, percentile 70%
public exploits
0
none known

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.

Patch / fix

  • packagist symfony/http-kernel 5.3.12
  • packagist symfony/symfony 5.3.12
  • bitnami symfony 5.3.12
  • sensiolabs symfony 5.3.12

Is CVE-2021-41267 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Exploit prediction

1.28% chance of exploitation in the next 30 days, higher than 70% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
GitHub 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N
OSV 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
packagist symfony/http-kernel
>=5.2.0, <5.3.12
5.3.12
packagist symfony/symfony
>=5.2.0, <5.3.12
5.3.12
bitnami symfony
>=5.2.0, <5.3.12
5.3.12

Affected products

  • symfony symfony

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.