What’s Vulnerable › Vulnerabilities

CVE-2020-15811

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 4.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-09-02 · updated 2026-06-17
• Weakness: CWE-697

Description

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4. Due to incorrect data validation, HTTP Request Splitting attacks may succeed against HTTP and HTTPS traffic. This leads to cache poisoning. This allows any client, including browser scripts, to bypass local security and poison the browser cache and any downstream caches with content from an arbitrary source. Squid uses a string search instead of parsing the Transfer-Encoding header to find chunked encoding. This allows an attacker to hide a second request inside Transfer-Encoding: it is interpreted by Squid as chunked and split out into a second request delivered upstream. Squid will then deliver two distinct responses to the client, corrupting any downstream caches.

Affected products

• Canonical Ubuntu Linux: 16.04, 18.04, 20.04
• Debian Linux: 9.0, 10.0
• Fedoraproject Fedora: 31, 32, 33
• openSUSE Leap: 15.1, 15.2
• Squid: before 4.13; from 5.0 before 5.0.4 — fixed in 4.13, 5.0.4

How to fix

Upgrade to a fixed version: Squid 4.13, 5.0.4. Check the vendor advisory for mitigations.

References

• http://lists.opensuse.org/opensuse-security-announce/2020-09/msg00012.html
• http://lists.opensuse.org/opensuse-security-announce/2020-09/msg00017.html
• https://github.com/squid-cache/squid/security/advisories/GHSA-c7p8-xqhm-49wv
• https://lists.debian.org/debian-lts-announce/2020/10/msg00005.html
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BE6FKUN7IGTIR2MEEMWYDT7N5EJJLZI2/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BMTFLVB7GLRF2CKGFPZ4G4R5DIIPHWI3/
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HJJDI7JQFGQLVNCKMVY64LAFMKERAOK7/
• https://security.netapp.com/advisory/ntap-20210219-0007/
• https://security.netapp.com/advisory/ntap-20210226-0006/
• https://security.netapp.com/advisory/ntap-20210226-0007/
• https://usn.ubuntu.com/4477-1/
• https://usn.ubuntu.com/4551-1/

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