Skip to content
Fencer Vulns
medium 6.5

CVE-2021-33620 json

Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause a denial of service (affecting availability to all clients) via an HT…

published 2021-05-28 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-20299

cvss
6.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
79.6%
EPSS 79.6% chance of exploitation in 30 days, percentile 99.6%
public exploits
0
none known

Summary

Squid before 4.15 and 5.x before 5.0.6 allows remote servers to cause a denial of service (affecting availability to all clients) via an HTTP response. The issue trigger is a header that can be expected to exist in HTTP traffic without any malicious intent by the server.

Patch / fix

  • squid-cache squid 4.15, 5.0.6
  • squid Debian 14, Debian 13, Debian 12 4.13-10

debian advisories DEBIAN-CVE-2021-33620

  • squid Ubuntu 20.04 LTS 4.10-1ubuntu1.4
  • squid3 Ubuntu 18.04 LTS 3.5.27-1ubuntu1.11

ubuntu advisories UBUNTU-CVE-2021-33620

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

red hat advisories RHSA-2021:4292

  • squid SLES for SAP 15 SP2, SLES for SAP 15 SP1, SLES for SAP 15 +18 more 4.17-150000.5.32.1
  • squid SLES for SAP 12 SP5, SLES 12 SP5 4.17-4.24.1

suse advisories SUSE-SU-2022:2553-1SUSE-SU-2022:2367-1

  • squid openSUSE Tumbleweed 5.4.1-2.1

opensuse advisories openSUSE-SU-2024:11929-1

  • 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 3.24, Alpine 3.23, Alpine 3.22 +7 more 5.0.6-r0

alpine advisories ALPINE-CVE-2021-33620

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

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-2021-33620 updated cvss 6.5

squid: denial of service in HTTP response processing

  • Red Hat Enterprise Linux 6 squid, squid34 Red Hat Enterprise Linux 7 squid, squid-sysvinit, squid-migration-script
    affected: workaround, no fix planned “Out of support scope”
  • 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+36416a77
    fixed: vendor fix RHSA-2021:4292
  • Red Hat Enterprise Linux 9 squid
    not 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

79.58% chance of exploitation in the next 30 days, higher than 99.6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.5 CVSS:3.1/AC:L/AV:N/A:H/C:N/I:N/PR:L/S:U/UI:N
CNA 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 4.0 AV:N/AC:L/Au:S/C:N/I:N/A:P

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

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.