CVE-2021-3564 Use after free in kernel

What is CVE-2021-3564?

CVE-2021-3564 is a medium-severity use after free vulnerability in Debian Debian Linux, published on 8 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

A flaw double-free memory corruption in the Linux kernel HCI device initialization subsystem was found in the way user attach malicious HCI TTY Bluetooth device. A local user could use this flaw to crash the system. This flaw affects all the Linux kernel versions starting from 3.13.

Weakness: CWE-415

Which versions are affected by CVE-2021-3564?

It affects 3 products.

Products include Debian Debian Linux, Fedoraproject Fedora, Linux kernel.

How do I fix CVE-2021-3564?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2021-3564 being exploited?

There is no known exploitation of CVE-2021-3564 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
• How this page is made

Also known as AZL-34858, AZL-6573, DEBIAN-CVE-2021-3564, GHSA-x4rf-jx7j-r49m, UBUNTU-CVE-2021-3564.