CVE-2009-3560 in iTunes
Summary
by MITRE
The big2_toUtf8 function in lib/xmltok.c in libexpat in Expat 2.0.1, as used in the XML-Twig module for Perl, allows context-dependent attackers to cause a denial of service (application crash) via an XML document with malformed UTF-8 sequences that trigger a buffer over-read, related to the doProlog function in lib/xmlparse.c, a different vulnerability than CVE-2009-2625 and CVE-2009-3720.
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Analysis
by VulDB Data Team • 11/24/2022
The vulnerability identified as CVE-2009-3560 represents a critical buffer over-read condition within the Expat XML parsing library version 2.0.1, specifically affecting the big2_toUtf8 function in lib/xmltok.c. This flaw occurs during XML document processing when malformed UTF-8 sequences are encountered, creating a scenario where the application fails to properly validate input data before attempting to read beyond allocated memory boundaries. The vulnerability is particularly concerning because it operates in a context-dependent manner, meaning that the malicious input must be carefully crafted to trigger the specific conditions that lead to the buffer over-read. The attack vector involves XML documents containing specially constructed malformed UTF-8 sequences that cause the parser to access memory locations beyond the intended buffer limits during the processing phase.
The technical implementation of this vulnerability stems from the doProlog function in lib/xmlparse.c which interfaces with the big2_toUtf8 function in lib/xmltok.c, creating a chain of operations that fails to properly validate UTF-8 sequence boundaries. When the parser encounters malformed UTF-8 data, the big2_toUtf8 function attempts to process these sequences without adequate bounds checking, leading to memory access violations that manifest as application crashes. This represents a classic buffer over-read vulnerability that falls under CWE-125, which specifically addresses out-of-bounds read conditions in software implementations. The vulnerability's context-dependent nature means that attackers must construct XML documents with precise malformed UTF-8 patterns that will trigger the specific memory access violation during parsing operations.
The operational impact of CVE-2009-3560 extends beyond simple application instability to potentially enable more sophisticated attacks when combined with other vulnerabilities or when the affected system has additional attack surface components. When exploited, this vulnerability can cause denial of service conditions that may disrupt legitimate XML processing operations within applications using the affected Expat library version. The vulnerability affects not only standalone applications but also systems that rely on XML-Twig module for Perl, which is commonly used in web applications, data processing systems, and enterprise environments where XML parsing is a fundamental component of data handling operations. The attack requires minimal privileges and can be executed through standard XML document submission, making it particularly dangerous in web-facing applications or systems that process untrusted XML input from external sources.
Mitigation strategies for CVE-2009-3560 should prioritize immediate patching of affected systems with updated versions of the Expat library that contain fixes for the buffer over-read condition. Organizations should implement comprehensive input validation measures that filter malformed XML content before it reaches the parser, using techniques such as schema validation or XML security policies that prevent the processing of potentially malicious input sequences. The vulnerability aligns with ATT&CK technique T1210 which involves exploiting weaknesses in software to cause denial of service or system compromise, and should be addressed as part of broader security hardening efforts. Network-based mitigations such as XML firewalls or content filtering systems can provide additional protection layers, while application-level defenses should include proper error handling and memory management practices that prevent buffer over-read conditions from causing system instability. Regular security assessments and vulnerability scanning should be implemented to identify systems running affected versions of Expat and ensure timely remediation of this and similar vulnerabilities.