What’s Vulnerable › Vulnerabilities

CVE-2020-15810

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.4% 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-444

Description

An issue was discovered in Squid before 4.13 and 5.x before 5.0.4. Due to incorrect data validation, HTTP Request Smuggling 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 proxy cache and any downstream caches with content from an arbitrary source. When configured for relaxed header parsing (the default), Squid relays headers containing whitespace characters to upstream servers. When this occurs as a prefix to a Content-Length header, the frame length specified will be ignored by Squid (allowing for a conflicting length to be used from another Content-Length header) but relayed upstream.

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-3365-q9qx-f98m
• 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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