CVE-2021-3682 Use after free in QEMU

What is CVE-2021-3682?

CVE-2021-3682 is a high-severity use after free vulnerability in Debian Debian Linux, published on 5 Aug 2021. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

A flaw was found in the USB redirector device emulation of QEMU in versions prior to 6.1.0-rc2. It occurs when dropping packets during a bulk transfer from a SPICE client due to the packet queue being full. A malicious SPICE client could use this flaw to make QEMU call free() with faked heap chunk metadata, resulting in a crash of QEMU or potential code execution with the privileges of the QEMU process on the host.

Weakness: CWE-763

Which versions are affected by CVE-2021-3682?

It affects 3 products.

Products include Debian Debian Linux, Qemu Qemu, Redhat Enterprise Linux.

How do I fix CVE-2021-3682?

Upgrade to a fixed version.

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-2021-3682 being exploited?

There is no known exploitation of CVE-2021-3682 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 AZL-6830, DEBIAN-CVE-2021-3682, GHSA-2w4j-r5v6-3vgr, OESA-2021-1316, UBUNTU-CVE-2021-3682.