Quick answers
- Is CVE-2026-76957 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-76957 being exploited in the wild.
- How severe is CVE-2026-76957?
- Medium severity, with a CVSS score of 4.9, published 20 August 2026.
- Which products and versions are affected?
- libexpat expat before 2.8.4.
- Is there a fix for CVE-2026-76957?
- A patch was published on 2026-08-31: libexpat 2.8.4 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-76957 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-76957?
- Check whether you run Libexpat Project Libexpat. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability is a use-after-free condition in libexpat's custom encoding callback handling, caused by insufficient handler call depth tracking when custom XML_Encoding.convert and XML_Encoding.release callbacks are invoked. The root cause is that these application-provided callbacks were not subject to the same parser re-entrancy protections that guard other handler callbacks, allowing a malicious XML document to trigger nested parser calls that free memory while it is still in use. An attacker must provide specially crafted XML to an application that implements custom encoding callbacks; no authentication is required and the attack is network-accessible. The fix, released in libexpat 2.8.4, wraps the custom encoding callbacks with Expat's existing handler reentrancy counter to enforce the same re-entry rejection rules applied to other callbacks.
Affected products
- libexpat expat before 2.8.4
Timeline
- 2026-08-20: disclosed
- 2026-08-31: patched: libexpat 2.8.4 released