CVE-2016-4472 in iTunes
Summary
by MITRE
The overflow protection in Expat is removed by compilers with certain optimization settings, which allows remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via crafted XML data. NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-1283 and CVE-2015-2716.
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Analysis
by VulDB Data Team • 08/02/2025
The vulnerability described in CVE-2016-4472 represents a critical flaw in the Expat XML parser library that emerged from an incomplete remediation of previous security issues. This vulnerability specifically targets the overflow protection mechanisms that were previously implemented to prevent buffer overflows during XML parsing operations. The flaw manifests when compilers apply certain optimization settings that inadvertently strip away the protective measures designed to safeguard against malicious input. The root cause lies in the compiler optimization process which can eliminate overflow checks during code compilation, creating a dangerous condition where XML parsers become susceptible to malicious input patterns that could trigger buffer overflows.
The technical implementation of this vulnerability exploits the interaction between compiler optimization levels and the underlying buffer management within the Expat parser. When specific optimization flags are enabled during compilation, the compiler may optimize away bounds checking code that was intended to prevent memory corruption during XML parsing. This optimization-induced removal of overflow protection creates a scenario where crafted XML data containing malformed structures can cause stack-based buffer overflows, leading to unpredictable behavior including program crashes or potentially arbitrary code execution. The vulnerability is particularly concerning because it can be triggered through standard XML parsing operations without requiring special privileges or complex attack vectors.
From an operational perspective, this vulnerability presents significant risk to systems that rely on Expat for XML processing, including web applications, enterprise software, and network services that parse XML content from untrusted sources. Attackers can leverage this vulnerability to perform denial of service attacks by causing applications to crash through carefully crafted XML payloads, or in more severe cases, potentially execute arbitrary code on vulnerable systems. The impact extends across multiple platforms and applications that utilize the Expat library, making it a widespread concern for organizations maintaining software systems that process XML data from external sources. The vulnerability's persistence is exacerbated by the fact that it can be triggered simply by enabling certain compiler optimization settings, making it difficult to predict and prevent in environments where optimization is routinely applied.
Organizations facing this vulnerability should implement immediate mitigation strategies including disabling problematic compiler optimizations for Expat-dependent applications, applying the latest available patches from the Expat maintainers, and implementing input validation measures to filter potentially malicious XML content. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and demonstrates characteristics consistent with ATT&CK technique T1203, involving the exploitation of input validation vulnerabilities to achieve arbitrary code execution. System administrators should also consider implementing network-level protections and monitoring for unusual XML parsing activity that might indicate exploitation attempts, while ensuring that all affected applications undergo thorough security testing after applying patches to verify that the vulnerability has been fully addressed.