libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.
CVE-2026-76957 is fixed in 11 products on 1 platform, first by expat 2.2.5-3ubuntu0.9+esm5, released August 20, 2026. It is not reported as exploited. Patch Radar priority: High.
libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.
Where it's fixed
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| MozillaFirefox · opensuse-leap 16.0 | 153.5.0-160000.1.1 | OPENSUSE-SU-2026:22139-1 | Nov 7, 2026 |
| MozillaFirefox · sles 15.6 | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 | Nov 7, 2026 |
| MozillaFirefox · sles 15.7 | 153.5.0-150400.157.16.1 | SUSE-SU-2026:4834-1 | Nov 7, 2026 |
| MozillaFirefox · sles 16.0 | 153.5.0-160000.1.1 | SUSE-SU-2026:24260-1 | Nov 7, 2026 |
| MozillaThunderbird · sles 15.7 | 153.5.0-150400.13.9.1 | SUSE-SU-2026:4736-1 | Nov 7, 2026 |
| expat · Debian 12.15 (bookworm) | 2.5.0-1+deb12u3 | DEBIAN-CVE-2026-76957 | Sep 1, 2026 |
| expat · Debian 13.5 (trixie) | 2.9.0-1~deb13u1 | DEBIAN-CVE-2026-76957 | Sep 1, 2026 |
| expat · Debian 14 | 2.8.4-1 | DEBIAN-CVE-2026-76957 | Sep 1, 2026 |
| expat · Ubuntu 18.04.6 LTS (bionic) | 2.2.5-3ubuntu0.9+esm5 | expat 2.2.5-3ubuntu0.9+esm5 | Aug 20, 2026 |
| expat · Ubuntu 20.04 LTS (focal) | 2.2.9-1ubuntu0.8+esm3 | expat 2.2.9-1ubuntu0.8+esm3 | Aug 20, 2026 |
| expat · Ubuntu 22.04.1 LTS (jammy) | 2.4.7-1ubuntu0.9 | expat 2.4.7-1ubuntu0.9 | Aug 20, 2026 |
| expat · Ubuntu 24.04.5 LTS (noble) | 2.6.1-2ubuntu0.6 | expat 2.6.1-2ubuntu0.6 | Aug 20, 2026 |
| expat · Ubuntu 26.04.1 LTS (resolute) | 2.7.4-1ubuntu0.2 | expat 2.7.4-1ubuntu0.2 | Aug 20, 2026 |
| expat · amzn 2023 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 | Sep 14, 2026 |
| expat · opensuse-leap 16.0 | 2.8.4-160000.1.1 | OPENSUSE-SU-2026:21945-1 | Sep 24, 2026 |
| expat · sles 15.6 | 2.8.5-150400.3.40.1 | SUSE-SU-2026:4623-1 | Nov 7, 2026 |
| expat · sles 15.7 | 2.8.5-150700.3.15.1 | SUSE-SU-2026:4619-1 | Nov 7, 2026 |
| expat · sles 16.0 | 2.8.4-160000.1.1 | SUSE-SU-2026:23912-1 | Sep 24, 2026 |
| expat-debuginfo · amzn 2023 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 | Sep 14, 2026 |
| expat-debugsource · amzn 2023 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 | Sep 14, 2026 |
| expat-devel · amzn 2023 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 | Sep 14, 2026 |
| expat-static · amzn 2023 | 2.8.3-1.amzn2023.0.1 | ALAS2023-2026-2157 | Sep 14, 2026 |
| firefox · amzn 2023 | 140.14.0-1.amzn2023.0.1 | ALAS2023-2026-2105 | Aug 31, 2026 |
| firefox-debuginfo · amzn 2023 | 140.14.0-1.amzn2023.0.1 | ALAS2023-2026-2105 | Aug 31, 2026 |
| firefox-debugsource · amzn 2023 | 140.14.0-1.amzn2023.0.1 | ALAS2023-2026-2105 | Aug 31, 2026 |
| libexpat1 · Ubuntu 18.04.6 LTS (bionic) | 2.2.5-3ubuntu0.9+esm5 | libexpat1 2.2.5-3ubuntu0.9+esm5 | Aug 20, 2026 |
| libexpat1 · Ubuntu 20.04 LTS (focal) | 2.2.9-1ubuntu0.8+esm3 | libexpat1 2.2.9-1ubuntu0.8+esm3 | Aug 20, 2026 |
| libexpat1 · Ubuntu 22.04.1 LTS (jammy) | 2.4.7-1ubuntu0.9 | libexpat1 2.4.7-1ubuntu0.9 | Aug 20, 2026 |
| libexpat1 · Ubuntu 24.04.5 LTS (noble) | 2.6.1-2ubuntu0.6 | libexpat1 2.6.1-2ubuntu0.6 | Aug 20, 2026 |
| libexpat1 · Ubuntu 26.04.1 LTS (resolute) | 2.7.4-1ubuntu0.2 | libexpat1 2.7.4-1ubuntu0.2 | Aug 20, 2026 |
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