CVE catalog

CVE-2021-28651

squid: CVE-2021-28651

Severity: High · CVSS 7.4CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:N/A:H
Published: May 10, 2021, 12:00:00 AM UTC
Source: [NVD] · [CVE record]
EPSS: 7.45% · Oct 25, 2026

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.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	squid	sid	`7.7-1`	fixed
Debian	squid	forky	`7.7-1`	fixed
Debian	squid	trixie	`6.13-2+deb13u3`	fixed
Debian	squid	trixie-security	`6.13-2+deb13u2`	fixed
Debian	squid	bookworm	`5.7-2+deb12u5`	fixed
Debian	squid	bookworm-security	`5.7-2+deb12u6`	fixed
Alpine	squid	3.10	`4.15-r0`	fixed
Alpine	squid	3.11	`4.15-r0`	fixed
Alpine	squid	3.12	`4.15-r0`	fixed
Alpine	squid	3.13	`5.0.6-r0`	fixed
Alpine	squid	3.14	`5.0.6-r0`	fixed
Alpine	squid	3.15	`5.0.6-r0`	fixed
Alpine	squid	3.16	`5.0.6-r0`	fixed
Alpine	squid	3.17	`5.0.6-r0`	fixed
Alpine	squid	3.18	`5.0.6-r0`	fixed
Alpine	squid	3.19	`5.0.6-r0`	fixed
Alpine	squid	3.20	`5.0.6-r0`	fixed
Alpine	squid	3.21	`5.0.6-r0`	fixed
Alpine	squid	3.22	`5.0.6-r0`	fixed
Alpine	squid	3.23	`5.0.6-r0`	fixed
Alpine	squid	3.24	`5.0.6-r0`	fixed
Ubuntu	squid3	pro	`3.5.23-5ubuntu1`	vulnerable
Ubuntu	squid3	pro	`3.5.23-5ubuntu2`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.1`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.2`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.3`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.4`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.5`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.6`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.7`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.8`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.9`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.10`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.11`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.12`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.13`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.14`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.14+esm1`	vulnerable
Ubuntu	squid3	pro	`3.5.27-1ubuntu1.14+esm2`	fixed
Ubuntu	squid3	18.04	`3.5.23-5ubuntu1`	vulnerable
Ubuntu	squid3	18.04	`3.5.23-5ubuntu2`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.1`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.2`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.3`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.4`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.5`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.6`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.7`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.8`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.9`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.10`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.11`	fixed
Ubuntu	squid	20.04	`4.8-1ubuntu2`	vulnerable
Ubuntu	squid	20.04	`4.8-1ubuntu3`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu1`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu2`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu3`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu4`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.1`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.2`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.3`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.4`	fixed
Ubuntu	squid3	pro	`3.3.8-1ubuntu16`	vulnerable
Ubuntu	squid3	pro	`3.3.8-1ubuntu17`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu6`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.1`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.2`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.3`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.4`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.5`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.6`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.7`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.8`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.9`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.10`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.11`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.12`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.13`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.14`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.15`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.16`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.16+esm1`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.16+esm2`	vulnerable
Ubuntu	squid3	pro	`3.5.12-1ubuntu7.16+esm3`	fixed
Ubuntu	squid3	18.04	`3.5.23-5ubuntu1`	vulnerable
Ubuntu	squid3	18.04	`3.5.23-5ubuntu2`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.1`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.2`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.3`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.4`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.5`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.6`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.7`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.8`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.9`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.10`	vulnerable
Ubuntu	squid3	18.04	`3.5.27-1ubuntu1.11`	fixed
Ubuntu	squid	20.04	`4.8-1ubuntu2`	vulnerable
Ubuntu	squid	20.04	`4.8-1ubuntu3`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu1`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu2`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu3`	vulnerable
Ubuntu	squid	20.04	`4.9-2ubuntu4`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.1`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.2`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.3`	vulnerable
Ubuntu	squid	20.04	`4.10-1ubuntu1.4`	fixed

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	squid	source	sid	`4.13-10`	not yet assigned	Not reported	[988893]
Debian	squid	source	forky	`4.13-10`	not yet assigned	Not reported	[988893]
Debian	squid	source	trixie	`4.13-10`	not yet assigned	Not reported	[988893]
Debian	squid	source	bookworm	`4.13-10`	not yet assigned	Not reported	[988893]
Alpine	squid	apk	3.10	`4.15-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.11	`4.15-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.12	`4.15-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.13	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.14	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.15	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.16	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.17	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.18	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.19	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.20	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.21	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.22	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.23	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Alpine	squid	apk	3.24	`5.0.6-r0`	Not reported	ALPINE-CVE-2021-28651	Not reported
Ubuntu	squid3	deb	pro	`3.5.27-1ubuntu1.14+esm2`	Not reported	USN-6857-1	Not reported
Ubuntu	squid3	deb	18.04	`3.5.27-1ubuntu1.11`	Not reported	USN-4981-1	Not reported
Ubuntu	squid	deb	20.04	`4.10-1ubuntu1.4`	Not reported	USN-4981-1	Not reported
Ubuntu	squid3	deb	pro	`3.5.12-1ubuntu7.16+esm3`	Not reported	UBUNTU-CVE-2021-28651	Not reported
Ubuntu	squid3	deb	18.04	`3.5.27-1ubuntu1.11`	Not reported	UBUNTU-CVE-2021-28651	Not reported
Ubuntu	squid	deb	20.04	`4.10-1ubuntu1.4`	Not reported	UBUNTU-CVE-2021-28651	Not reported

[Debian bug #988893]

OpenFactory catalog packages

Matching against OpenFactory catalog package versions is in progress.

[Debian 12 (Bookworm)]

[squid]Unknown
Details (4)
- 5.7-2+deb12u5 · amd64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · arm64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · amd64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · arm64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
[squid-cgi]Unknown
Source package: [squid]
Details (4)
- 5.7-2+deb12u5 · amd64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · arm64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · amd64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · arm64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
[squidclient]Unknown
Source package: [squid]
Details (4)
- 5.7-2+deb12u5 · amd64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · arm64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · amd64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · arm64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
[squid-common]Unknown
Source package: [squid]
Details (4)
- 5.7-2+deb12u5 · all · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · all · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · all · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · all · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
[squid-openssl]Unknown
Source package: [squid]
Details (4)
- 5.7-2+deb12u5 · amd64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · arm64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · amd64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · arm64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
[squid-purge]Unknown
Source package: [squid]
Details (4)
- 5.7-2+deb12u5 · amd64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u5 · arm64 · bookworm
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · amd64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12
- 5.7-2+deb12u6 · arm64 · bookworm-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · bookworm; dsa · squid · debian · 12

[Debian 13 (Trixie)]

[squid]Unknown
Details (4)
- 6.13-2+deb13u2 · amd64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
[squid-cgi]Unknown
Source package: [squid]
Details (4)
- 6.13-2+deb13u2 · amd64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
[squidclient]Unknown
Source package: [squid]
Details (4)
- 6.13-2+deb13u2 · amd64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
[squid-common]Unknown
Source package: [squid]
Details (4)
- 6.13-2+deb13u2 · all · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · all · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · all · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · all · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
[squid-openssl]Unknown
Source package: [squid]
Details (4)
- 6.13-2+deb13u2 · amd64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
[squid-purge]Unknown
Source package: [squid]
Details (4)
- 6.13-2+deb13u2 · amd64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · amd64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13
- 6.13-2+deb13u2 · arm64 · trixie-security
  Fixed · Fixed: 4.13-10
  dsa · squid · debian · 13

Observed: Oct 23, 2026, 5:55:30 PM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX]