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.
Weakness
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Libexpat | Libexpat_project | * | 2.8.4 (excluding) |
| Red Hat Hardened Images | RedHat | expat-main-2.8.3-0.1.1.hum1 | * |
| Red Hat Hardened Images | RedHat | expat-main-2.8.4-0.1.hum1 | * |
| Expat | Ubuntu | devel | * |
| Expat | Ubuntu | esm-infra-legacy/trusty | * |
| Expat | Ubuntu | esm-infra-legacy/xenial | * |
| Expat | Ubuntu | esm-infra/bionic | * |
| Expat | Ubuntu | esm-infra/focal | * |
| Expat | Ubuntu | jammy | * |
| Expat | Ubuntu | noble | * |
| Expat | Ubuntu | resolute | * |
| Expat | Ubuntu | upstream | * |
| Matanza | Ubuntu | devel | * |
| Matanza | Ubuntu | esm-apps/focal | * |
| Matanza | Ubuntu | esm-apps/jammy | * |
| Matanza | Ubuntu | esm-apps/noble | * |
| Matanza | Ubuntu | esm-apps/resolute | * |
| Matanza | Ubuntu | jammy | * |
| Matanza | Ubuntu | noble | * |
| Matanza | Ubuntu | resolute | * |