CVE-2021-20317 Denial of service in kernel

What is CVE-2021-20317?

CVE-2021-20317 is a medium-severity denial of service vulnerability in Debian Debian Linux, published on 27 Sep 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

A flaw was found in the Linux kernel. A corrupted timer tree caused the task wakeup to be missing in the timerqueue_add function in lib/timerqueue.c. This flaw allows a local attacker with special user privileges to cause a denial of service, slowing and eventually stopping the system while running OSP.

Weakness: CWE-665

Which versions are affected by CVE-2021-20317?

It affects 2 products.

Products include Debian Debian Linux, Linux kernel.

How do I fix CVE-2021-20317?

Apply the vendor's patch.

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-2021-20317 being exploited?

There is no known exploitation of CVE-2021-20317 in the wild and no public exploit code.

Other vulnerabilities in Debian Debian Linux

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• 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 DEBIAN-CVE-2021-20317, GHSA-hf76-5hm2-g68j, UBUNTU-CVE-2021-20317.