CVE-2021-28651 json
An issue was discovered in Squid before 4.15 and 5.x before 5.0.6.
published 2021-05-27 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-15320
- cvss
- 7.5
- version 3.1, NVD
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 7.4%
- EPSS 7.4% chance of exploitation in 30 days, percentile 94%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- squid-cache squid 4.15, 5.0.6
- squid Debian 14, Debian 13, Debian 12 4.13-10
debian advisories DEBIAN-CVE-2021-28651
- squid Ubuntu 20.04 LTS 4.10-1ubuntu1.4
- squid3 Ubuntu 18.04 LTS 3.5.27-1ubuntu1.11
- squid3 Ubuntu Pro 16.04 LTS 3.5.12-1ubuntu7.16+esm3
ubuntu advisories UBUNTU-CVE-2021-28651
Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0
- squid RHEL 8 7:4.15-1.module+el8.5.0+11469+24c223d9
- libecap RHEL 8 1.0.1-2.module+el8.1.0+4044+36416a77
- squid RHEL 7 ELS 7:3.5.20-17.el7_9.14
- squid-sysvinit RHEL 7 ELS 7:3.5.20-17.el7_9.14
- squid-migration-script RHEL 7 ELS 7:3.5.20-17.el7_9.14
red hat advisories RHSA-2025:14414RHSA-2021:4292
- squid SLES for SAP 12 SP4, SLES 12 SP4-LTSS, SLES 12 SP3-BCL +3 more 3.5.21-26.35.1
- squid3 SLES 11 SP4-LTSS, SLE Point of Sale 11 SP3 3.1.23-8.16.37.18.1
- squid SLES for SAP 15 SP1, SLES for SAP 15, SLES 15-LTSS +12 more 4.15-5.26.1
- squid SLES for SAP 12 SP5, SLES 12 SP5 4.15-4.18.1
suse advisories SUSE-SU-2022:2392-1SUSE-SU-2022:14914-1SUSE-SU-2021:1961-1SUSE-SU-2021:1838-1
- squid openSUSE Tumbleweed 4.16-1.5
- squid openSUSE Leap 15.3 4.15-5.26.1
- squid openSUSE Leap 15.2 4.15-lp152.2.9.1
opensuse advisories openSUSE-SU-2024:11403-1openSUSE-SU-2021:1961-1openSUSE-SU-2021:0879-1
- squid AlmaLinux 8 7:4.15-3.module_el8.6.0+3010+383bc947.1
- libecap AlmaLinux 8 1.0.1-2.module_el8.6.0+2741+01592ae8
almalinux advisories ALSA-2021:4292
- squid Rocky Linux 8 7:4.15-1.module+el8.5.0+705+218dec94
- libecap Rocky Linux 8 1.0.1-2.module+el8.4.0+404+316a0dc5
rocky linux advisories RLSA-2021:4292
- squid Alpine 3.12, Alpine 3.11, Alpine 3.10 4.15-r0
- squid Alpine 3.24, Alpine 3.23, Alpine 3.22 +9 more 5.0.6-r0
alpine advisories ALPINE-CVE-2021-28651
Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0
- squid Arch Linux 4.15-1
arch linux advisories AVG-1949
Vendor advisories
What the vendors themselves say about their products: affected, fixed or not affected, and what to do.
red hat product security vex CVE-2021-28651 updated cvss 7.4
squid: denial of service in URN processing
-
Red Hat Enterprise Linux 6 squid, squid34affected: workaround, no fix planned “If possible, disable URN processing by adding the following lines in `squid.conf`: ``` acl URN proto URN http_access deny URN ```”
-
Red Hat Enterprise Linux AppStream (v. 8) squid 4.15-1.module+el8.5.0+11469+24c223d9, libecap 1.0.1-2.module+el8.1.0+4044+36416a77fixed: vendor fix “If possible, disable URN processing by adding the following lines in `squid.conf`: ``` acl URN proto URN http_access deny URN ```” RHSA-2021:4292
-
Red Hat Enterprise Linux Server (v. 7 ELS) squid 3.5.20-17.el7_9.14, squid-migration-script 3.5.20-17.el7_9.14 Red Hat Enterprise Linux Server Optional (v. 7 ELS) squid-sysvinit 3.5.20-17.el7_9.14fixed: vendor fix “If possible, disable URN processing by adding the following lines in `squid.conf`: ``` acl URN proto URN http_access deny URN ```” RHSA-2025:14414
-
Red Hat Enterprise Linux 9 squidnot affected: vulnerable code not present
Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf
Exploit prediction
7.45% chance of exploitation in the next 30 days, higher than 94% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- bugs.squid-cache.org https://bugs.squid-cache.org/show_bug.cgi?id=5104 referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| NVD | 3.1 | 7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVD | 2.0 | 5.0 | AV:N/AC:L/Au:N/C:N/I:N/A:P |
Classification
- Weakness
-
- CWE-401 Missing Release of Memory after Effective Lifetime
References
-
github.com
/squid-cache/squid/security/advisories/GHSA-ch36-9jhx-phm4
patch, third-party-advisory
-
bugs.squid-cache.org
/show_bug.cgi?id=5104
exploit, issue-tracking, vendor-advisory
-
debian.org
/security/2021/dsa-4924
vendor-advisory, third-party-advisory
-
lists.fedoraproject.org
/archives/list/package-announce%40lists.fedoraproject.org/message/LSQ3U54ZCNXR44QRPW3AV2VCS6K3TKCF/
vendor-advisory
-
lists.fedoraproject.org
/archives/list/package-announce%40lists.fedoraproject.org/message/T4EPIWUZDJAXADDHVOPKRBTQHPBR6H66/
vendor-advisory
-
lists.debian.org
/debian-lts-announce/2021/06/msg00014.html
mailing-list, third-party-advisory
-
security.netapp.com
/advisory/ntap-20210716-0007/
third-party-advisory
-
openwall.com
/lists/oss-security/2023/10/11/3
mailing-list, third-party-advisory
-
seclists.org
/fulldisclosure/2023/Oct/14
mailing-list, third-party-advisory
Sources
- CVE List CVE-2021-28651
- NVD CVE-2021-28651
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.