CVE-2020-15673 Use after free in Firefox

What is CVE-2020-15673?

CVE-2020-15673 is a high-severity use after free vulnerability in Debian Debian Linux, published on 1 Oct 2020. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Mozilla developers reported memory safety bugs present in Firefox 80 and Firefox ESR 78.2. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.

Weakness: CWE-416

Which versions are affected by CVE-2020-15673?

It affects 5 products.

Products include Debian Debian Linux, Mozilla Firefox, Mozilla Firefox Esr, Mozilla Thunderbird, Opensuse Leap.

How do I fix CVE-2020-15673?

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-2020-15673 being exploited?

There is no known exploitation of CVE-2020-15673 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-2020-15673, GHSA-662r-59mf-5fxr, UBUNTU-CVE-2020-15673.