CVE-2021-33620 Denial of service in n/a

What is CVE-2021-33620?

CVE-2021-33620 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 28 May 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official 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.

Weakness: CWE-20

Which versions are affected by CVE-2021-33620?

It affects 3 products.

Products include Debian Debian Linux, Fedoraproject Fedora, Squid-Cache Squid.

How do I fix CVE-2021-33620?

Upgrade to a fixed version.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-33620 being exploited?

There is no known exploitation of CVE-2021-33620 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

• CVE-2015-3306 ProFTPD Improper Access Control Exploited Critical 10.0
• CVE-2025-49113 RoundCube Webmail Deserialization of Untrusted Data Exploited Critical 9.9
• CVE-2026-24061 GNU InetUtils Argument Injection Exploited Critical 9.8
• CVE-2025-39682 Linux Kernel Improper Check for Unusual or Exceptional Conditions Exploited Critical 9.8
• CVE-2024-9680 Mozilla Firefox Use-After-Free Exploited Critical 9.8

All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• GitHub advisory
• How this page is made

Also known as ALPINE-CVE-2021-33620, DEBIAN-CVE-2021-33620, GHSA-56g5-gjqr-cc85, GHSA-572g-rvwr-6c7f, UBUNTU-CVE-2021-33620, openSUSE-SU-2024:11929-1.