CVE-2021-33620

Name: CVE-2021-33620
Creator: NVD / NIST
Published: 2021-05-28T12:15:07.697+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 79.58%

Last modified Jun 17, 2026

CVE-2021-33620 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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.. EPSS estimates a 79.58% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1

6.5/10

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

EPSS Probability

79.58%

99.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-20

Affected Software

Vendor	Product	Versions
Squid-Cache	Squid	< 4.15
Squid-Cache	Squid	>= 5.0, < 5.0.6
Fedoraproject	Fedora	33
Fedoraproject	Fedora	34
Debian	Debian Linux	9.0

References

http://seclists.org/fulldisclosure/2023/Oct/14Mailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2023/10/11/3Mailing List, Third Party Advisory
http://www.squid-cache.org/Versions/v4/changesets/squid-4-1e05a85bd28c22c9ca5d3ac9f5e86d6269ec0a8c.patchMailing List, Patch, Vendor Advisory
http://www.squid-cache.org/Versions/v5/changesets/squid-5-8af775ed98bfd610f9ce762fe177e01b2675588c.patchMailing List, Patch, Vendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-572g-rvwr-6c7fPatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/06/msg00014.htmlMailing List, Third Party Advisory
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/
http://seclists.org/fulldisclosure/2023/Oct/14Mailing List, Third Party Advisory
http://www.openwall.com/lists/oss-security/2023/10/11/3Mailing List, Third Party Advisory
http://www.squid-cache.org/Versions/v4/changesets/squid-4-1e05a85bd28c22c9ca5d3ac9f5e86d6269ec0a8c.patchMailing List, Patch, Vendor Advisory
http://www.squid-cache.org/Versions/v5/changesets/squid-5-8af775ed98bfd610f9ce762fe177e01b2675588c.patchMailing List, Patch, Vendor Advisory
https://github.com/squid-cache/squid/security/advisories/GHSA-572g-rvwr-6c7fPatch, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2021/06/msg00014.htmlMailing List, Third Party Advisory
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/

Timeline

Published: May 28, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-33620?

How severe is CVE-2021-33620?

CVE-2021-33620 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 79.58% probability of exploitation in the next 30 days.

How do I fix CVE-2021-33620?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-33620?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST