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symfonySymfony SASSYMFONY:CVE-2021-41267-WEBCACHE-POISONING-VIA-X-FORWARDED-PREFIX-AND-SUB-REQUEST
HistoryNov 24, 2021 - 12:00 a.m.

CVE-2021-41267: Webcache Poisoning via X-Forwarded-Prefix and sub-request

2021-11-2400:00:00
Symfony SAS
symfony.com
9

4.3 Medium

CVSS2

Attack Vector

NETWORK

Attack Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

6.5 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

HIGH

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

6.1 Medium

AI Score

Confidence

High

0.001 Low

EPSS

Percentile

39.3%

Description

When a Symfony application is running behind a proxy or a load-balancer, you can tell Symfony to look for the X-Forwarded-* HTTP headers. HTTP headers that are not part of the β€œtrusted_headers” allowed list are ignored and protect you from β€œCache poisoning” attacks.

In Symfony 5.2, we’ve added support for the X-Forwarded-Prefix header, but this header was accessible in sub-requests, even if it was not part of the β€œtrusted_headers” allowed list. An attacker could leverage this opportunity to forge requests containing a X-Forwarded-Prefix HTTP header, leading to a web cache poisoning issue.

Resolution

Symfony now ensures that the X-Forwarded-Prefix HTTP header is not forwarded to sub-requests when it is not trusted.

The patch for this issue is available here for branch 5.3.

Credits

We would like to thank Soner Sayakci for reporting the issue and JΓ©rΓ©my DerussΓ© for fixing the issue.

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Published in #Security Advisories

4.3 Medium

CVSS2

Attack Vector

NETWORK

Attack Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

6.5 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

UNCHANGED

Confidentiality Impact

NONE

Integrity Impact

HIGH

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

6.1 Medium

AI Score

Confidence

High

0.001 Low

EPSS

Percentile

39.3%

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