Unrated

Use-after-free in libexpat XML_ResumeParser handler reentry

IdentifiersCVE-2026-56131CWE-416

CVE-2026-56131 is a use-after-free vulnerability in libexpat before 2.8.2. The issue arises because libexpat lacked handler call-depth tracking for calls to XML_ResumeParser made from within application-defined handlers when a policy violation condition exists. According to the provided context, this is a follow-on fix that plugs a gap in the remediation for CVE-2026-50219. In affected versions, reentrant invocation of XML_ResumeParser from a handler can violate parser state assumptions and lead to use of freed memory.

For your environment

Are you exposed to this one?

Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.

Start free trial

ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation can trigger a use-after-free condition in applications using vulnerable libexpat versions. This may result in process crashes, memory corruption, and potentially arbitrary code execution, depending on allocator behavior, exploitability of the surrounding application, and how libexpat is embedded and exposed to attacker-controlled XML input.

Mitigation

If you can’t patch tonight, do this now.

If immediate upgrade is not possible, avoid or prohibit calling XML_ResumeParser from within Expat handlers, especially in code paths that may be reached during parser policy-violation handling. Review bindings and wrapper code for reentrant parser API usage from callbacks, and reduce exposure to untrusted XML until patched. Complete mitigation information beyond this is not available in the provided content.

Remediation

Patch, then assume compromise.

Upgrade libexpat to version 2.8.2 or later, which adds protections around XML_ResumeParser being called from within handlers and closes this gap in the earlier CVE-2026-50219 fix.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

LibexpatExpatapplication

Libexpat ProjectLibexpatapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

8 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

8 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

Start free trial

Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity8

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2026-56131

NVD

nvd.nist.gov/vuln/detail/CVE-2026-56131

MITRE CWE · CWE-416

cwe.mitre.org