Cyber Resilience

CVE-2026-6653

XXE in Xmlsoft Libxml2 2.9.11 – 2.11.0

Public PoCXXEMemory Safety
Published
22 June 2026
Modified
14 July 2026
Patch / advisory
View advisory
CVSS Score v4 7.0
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0036 28th percentile
Risk Priority 55 floored blend · peak EPSS

Summary

CVE-2026-6653 is a high-severity Use After Free (CWE-416) vulnerability in Xmlsoft Libxml2. Its CVSS base score is 7.0 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 28th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A02:2025 Security Misconfiguration

EU & UK References

Vulnerability Data

Use After Free in libxml2's xmlParseInternalSubset from GNOME libxml2 version 2.9.11 to 2.11.0 allows a remote attacker to cause a denial-of-service via maliciously crafted XML input with improper entity resolution handling.

CWE(s)
CWE-416CWE-611

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 →
Why these techniques?

Remote DoS via crafted XML input to libxml2 enables exploitation of public-facing applications that parse untrusted XML.

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

Likely ATT&CK TechniquesAI

Techniques this vulnerability likely enables, inferred from its description, weakness type, and attributed-actor tradecraft. Confidence is per-technique.

T1499.004 Application or System Exploitation Impactconfidence: HIGH
UAF in XML parser directly enables remote DoS via crafted input to affected applications.
attack.mitre.org →
inferred from description + CWE · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2024-25062Same product: Xmlsoft Libxml2
CVE-2023-45322Same product: Xmlsoft Libxml2
CVE-2025-24855Same vendor: Xmlsoft
CVE-2024-55549Same vendor: Xmlsoft
CVE-2024-56171Same product: Xmlsoft Libxml2
CVE-2025-65482Shared CWE-611
CVE-2025-62788Shared CWE-416
CVE-2025-64518Shared CWE-611
CVE-2025-8355Shared CWE-611
CVE-2026-42530Shared CWE-416

Affected Assets

xmlsoft
libxml2
2.9.11 — 2.11.0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • SI-10 Information Input Validation
  • SI-2 Flaw Remediation
  • CM-7 Least Functionality
Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 3 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)
  • V1.4.3
  • V1.5.1
  • V15.3.2

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match
prevent

Directly enforces validation and sanitization of untrusted XML input to block the crafted entity structures that trigger the use-after-free in xmlParseInternalSubset.

SI-2 Flaw Remediation good match
prevent

Requires prompt application of patches or updates to libxml2 to eliminate the vulnerable xmlParseInternalSubset code path entirely.

CM-7 Least Functionality partial match
prevent

Restricts XML parser functionality (e.g., disabling external entity resolution) so that the CWE-611 trigger cannot be exercised even if malicious input arrives.

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-01 mostly match
prevents

Hardened XML parser configurations directly disable external entity resolution.

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.8.8 Management of technical vulnerabilities mostly match
detects

Vulnerability management identifies and patches XML libraries with unsafe default entity settings.

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.

References