Cyber Resilience

CVE-2026-56412

Memory Safety in Libexpat Project Libexpat ≤ 2.8.2

Memory Safety
Published
21 June 2026
Modified
23 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 4.9
Click a component to see what it means
Raw vectorCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
EPSS Score 0.0014 4th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-56412 is a medium-severity Use After Free (CWE-416) vulnerability in Libexpat Project Libexpat. Its CVSS base score is 4.9 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 4th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning) — see the control section below for these in your framework.

EU & UK References

Vulnerability Data

libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks handler call depth tracking for various calls from within handlers in cases of a policy violation. Thus, a use-after-free can occur. NOTE: this issue exists because of an…

more

incomplete fix for CVE-2026-50219.

CWE(s)
CWE-416

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
Why these techniques?

UAF in XML parser library enables RCE when parsing untrusted input, directly facilitating exploitation of public apps (T1190), client execution (T1203), or priv esc (T1068).

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-50219Same product: Libexpat Project Libexpat
CVE-2026-56131Same product: Libexpat Project Libexpat
CVE-2024-56171Shared CWE-416
CVE-2026-11634Shared CWE-416
CVE-2026-12029Shared CWE-416
CVE-2026-12014Shared CWE-416
CVE-2026-57076Shared CWE-416
CVE-2026-5874Shared CWE-416
CVE-2026-5289Shared CWE-416
CVE-2026-12440Shared CWE-416

Affected Assets

libexpat project
libexpat
≤ 2.8.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-2 Flaw Remediation
Detect
Catch it (NIST detect / respond)
  • SI-7 Software, Firmware, and Information Integrity
  • RA-5 Vulnerability Monitoring and Scanning
Harden
Shrink the surface (DISA STIG)
  • 3 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V1.4.3

Mitigating Controls (NIST 800-53 r5) AI

SI-2 Flaw Remediation good match
prevent

Directly requires applying the libexpat >=2.8.2 patch that completes the handler-depth tracking fix for the XML_TOK_DATA_CHARS path.

SI-7 Software, Firmware, and Information Integrity partial match
detect

Requires integrity verification of the expat binary/libraries so that an unpatched vulnerable instance can be detected before use.

RA-5 Vulnerability Monitoring and Scanning partial match
detect

Requires continuous vulnerability scanning that would flag the known incomplete fix for CVE-2026-50219 and the resulting CWE-416 in libexpat <2.8.2.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly incorporate memory-safety tooling and reviews that prevent most use-after-free defects.

ID.RA-01 partial match
prevents

Vulnerability identification processes can discover use-after-free issues via scanning or analysis but do not prevent their introduction.

PR.PS-02 partial match
prevents

Routine patching removes known use-after-free instances after they have been introduced in released software.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
detects

Security testing in development can detect use-after-free bugs before release.

A.8.25 Secure development life cycle partial match
prevents

Secure SDLC mandates memory-safety practices that reduce use-after-free defects.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify memory-management rules that mitigate use-after-free.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles include memory-safety design choices that limit use-after-free exposure.

A.8.28 Secure coding partial match
prevents

Secure coding standards directly prescribe avoidance of use-after-free patterns.

A.8.32 Change management partial match
prevents

Change-management processes help ensure memory-safety fixes are deployed consistently.

References