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Vulnerability record · CVE-2021-28651 · published 27 May 2021

CVE-2021-28651: Squid-cache squid memory leak vulnerability

Squid Cache · Squid

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.

7.5 CVSS 3.1 High EPSS 7.4% · top 5.8% CWE-401 · Memory leak
7.5CVSS 3.1 base score, v2 5.0
7.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
4Affected product versions listed by NVD
18References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

4 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://seclists.org/fulldisclosure/2023/Oct/14 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2023/10/11/3 Mailing ListThird Party Advisory
https://bugs.squid-cache.org/show_bug.cgi?id=5104 ExploitIssue TrackingVendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4 PatchThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/06/msg00014.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LSQ3U54ZCNXR44QRPW3AV2V
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/T4EPIWUZDJAXADDHVOPKRBT
https://security.netapp.com/advisory/ntap-20210716-0007/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4924 Third Party Advisory
http://seclists.org/fulldisclosure/2023/Oct/14 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2023/10/11/3 Mailing ListThird Party Advisory
https://bugs.squid-cache.org/show_bug.cgi?id=5104 ExploitIssue TrackingVendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4 PatchThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/06/msg00014.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LSQ3U54ZCNXR44QRPW3AV2V
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/T4EPIWUZDJAXADDHVOPKRBT
https://security.netapp.com/advisory/ntap-20210716-0007/ Third Party Advisory
https://www.debian.org/security/2021/dsa-4924 Third Party Advisory

Track CVE-2021-28651 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-28651), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.