CVE-2007-6284 in Solaris
Summary
by MITRE
The xmlCurrentChar function in libxml2 before 2.6.31 allows context-dependent attackers to cause a denial of service (infinite loop) via XML containing invalid UTF-8 sequences.
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Analysis
by VulDB Data Team • 08/03/2019
The vulnerability identified as CVE-2007-6284 affects the libxml2 library version 2.6.31 and earlier, representing a critical denial of service flaw that can be exploited through malformed XML input containing invalid UTF-8 sequences. This vulnerability resides within the xmlCurrentChar function which serves as a fundamental component in XML parsing operations. The flaw manifests when the library encounters XML documents with invalid UTF-8 byte sequences that trigger an infinite loop during character processing, effectively consuming system resources and rendering the application unresponsive.
The technical implementation of this vulnerability stems from insufficient validation of UTF-8 encoding within the xmlCurrentChar function. When processing XML content, libxml2 attempts to parse UTF-8 sequences to determine character boundaries and validate encoding correctness. However, the function fails to properly handle malformed UTF-8 sequences that do not conform to standard encoding rules, causing the parser to enter an infinite loop while attempting to process these invalid byte patterns. This behavior aligns with CWE-835, which specifically addresses infinite loops in software implementations, and demonstrates how improper input validation can lead to resource exhaustion attacks.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited by context-dependent attackers to consume significant system resources including CPU cycles and memory. Attackers can craft malicious XML documents containing carefully constructed invalid UTF-8 sequences that will cause vulnerable applications using libxml2 to enter continuous processing loops. This makes the vulnerability particularly dangerous in web applications, XML processing services, and any system that accepts XML input from untrusted sources, as a single malicious request can effectively bring the entire service to a halt. The vulnerability also aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion.
Mitigation strategies for CVE-2007-6284 primarily involve upgrading to libxml2 version 2.6.31 or later, where the vulnerability has been addressed through improved UTF-8 validation and proper loop termination handling. Organizations should also implement XML input validation and sanitization at application boundaries, employing XML parsers with built-in protection mechanisms against malformed input. Additionally, system administrators should consider implementing rate limiting and resource monitoring to detect and prevent exploitation attempts. The fix implemented in libxml2 2.6.31 specifically addresses the root cause by ensuring proper handling of invalid UTF-8 sequences and preventing the infinite loop condition through enhanced error detection and recovery mechanisms.