CVE-2021-28651

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 7.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-05-27 · updated 2026-06-17
Weakness: CWE-401

Description

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a buffer-management bug, it allows a denial of service. When resolving a request with the urn: scheme, the parser leaks a small amount of memory. However, there is an unspecified attack methodology that can easily trigger a large amount of memory consumption.

Affected products

Debian Linux: 9.0, 10.0
Fedoraproject Fedora: 33, 34
Cloud Manager: all versions
Squid: from 2.0 before 4.15; from 5.0 before 5.0.6 — fixed in 4.15, 5.0.6

How to fix

Upgrade to a fixed version: Squid 4.15, 5.0.6. Check the vendor advisory for mitigations.

References

http://seclists.org/fulldisclosure/2023/Oct/14
http://www.openwall.com/lists/oss-security/2023/10/11/3
https://bugs.squid-cache.org/show_bug.cgi?id=5104
https://github.com/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4
https://lists.debian.org/debian-lts-announce/2021/06/msg00014.html
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LSQ3U54ZCNXR44QRPW3AV2VCS6K3TKCF/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/T4EPIWUZDJAXADDHVOPKRBTQHPBR6H66/
https://security.netapp.com/advisory/ntap-20210716-0007/
https://www.debian.org/security/2021/dsa-4924
http://seclists.org/fulldisclosure/2023/Oct/14
http://www.openwall.com/lists/oss-security/2023/10/11/3
https://bugs.squid-cache.org/show_bug.cgi?id=5104

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