CVE-2021-31806 Denial of service in n/a

What is CVE-2021-31806?

CVE-2021-31806 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 27 May 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

An issue was discovered in Squid before 4.15 and 5.x before 5.0.6. Due to a memory-management bug, it is vulnerable to a Denial of Service attack (against all clients using the proxy) via HTTP Range request processing.

Weakness: CWE-116

Which versions are affected by CVE-2021-31806?

It affects 4 products.

Products include Debian Debian Linux, Fedoraproject Fedora, Netapp Cloud Manager, Squid-Cache Squid.

How do I fix CVE-2021-31806?

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-2021-31806 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-31806 exists.

Public exploit code: 1 Metasploit module.

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
• How this page is made

Also known as ALPINE-CVE-2021-31806, DEBIAN-CVE-2021-31806, GHSA-3v8m-hgx9-fgh9, UBUNTU-CVE-2021-31806.