CVE-2023-4049 Use after free in Firefox

What is CVE-2023-4049?

CVE-2023-4049 is a medium-severity use after free vulnerability in Debian Debian Linux, published on 1 Aug 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Race conditions in reference counting code were found through code inspection. These could have resulted in potentially exploitable use-after-free vulnerabilities. This vulnerability affects Firefox < 116, Firefox ESR < 102.14, and Firefox ESR < 115.1.

Weakness: CWE-362

Which versions are affected by CVE-2023-4049?

It affects 2 products.

Products include Debian Debian Linux, Mozilla Firefox.

How do I fix CVE-2023-4049?

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-2023-4049 being exploited?

There is no known exploitation of CVE-2023-4049 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 DEBIAN-CVE-2023-4049, GHSA-6jfh-jrm6-9hm8, UBUNTU-CVE-2023-4049.