CVE-2026-6653 in libxml2
Summary
by MITRE • 06/22/2026
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.
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Analysis
by VulDB Data Team • 06/22/2026
This vulnerability represents a critical use-after-free condition in the libxml2 library that affects GNOME applications and systems relying on this XML parsing component. The flaw exists within the xmlParseInternalSubset function which handles internal subset declarations in XML documents, specifically when processing maliciously crafted XML input containing improper entity resolution handling. The vulnerability arises from insufficient validation of entity references during XML parsing operations, creating a scenario where freed memory locations are accessed after the xmlParseInternalSubset function has completed its execution. This particular issue affects libxml2 versions ranging from 2.9.11 through 2.11.0, making it a widespread concern across numerous applications that depend on this library for XML processing. The root cause aligns with CWE-416 which describes use-after-free vulnerabilities where memory is accessed after it has been freed, and the exploitation pattern corresponds to ATT&CK technique T1203 related to exploitation for privilege escalation through memory corruption.
The operational impact of this vulnerability extends beyond simple denial-of-service conditions as remote attackers can leverage this flaw to potentially execute arbitrary code or cause system instability. When a malicious XML document is processed by an affected application, the improper entity resolution handling triggers the use-after-free condition during the parsing phase. This occurs because the xmlParseInternalSubset function fails to properly manage reference counts for entities that are freed before all references to them have been resolved. Applications utilizing libxml2 for XML processing including web browsers, email clients, and server applications become vulnerable when they encounter specially crafted XML content containing malformed entity declarations. The vulnerability can be triggered through various attack vectors such as web pages loading XML content, email attachments, or any application that parses external XML sources without proper input sanitization.
Mitigation strategies for this vulnerability require immediate patching of affected libxml2 versions to the latest releases where the memory management issues have been resolved. System administrators should prioritize updating all affected systems and applications that depend on libxml2, particularly those handling untrusted XML input from external sources. Additional defensive measures include implementing strict input validation for XML content, employing XML parsers with built-in security features, and configuring application-level restrictions to prevent processing of suspicious XML documents. Organizations should also consider deploying network-based intrusion detection systems to monitor for exploitation attempts targeting this vulnerability. The fix addresses the underlying memory management issue by ensuring proper reference counting and cleanup procedures during entity resolution processes, preventing the premature freeing of memory blocks that are still in use. Security teams must conduct comprehensive vulnerability assessments across their infrastructure to identify all applications using vulnerable libxml2 versions and implement remediation measures accordingly.