CVE-2016-4483 in tvOS
Summary
by MITRE
The xmlBufAttrSerializeTxtContent function in xmlsave.c in libxml2 allows context-dependent attackers to cause a denial of service (out-of-bounds read and application crash) via a non-UTF-8 attribute value, related to serialization. NOTE: this vulnerability may be a duplicate of CVE-2016-3627.
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Analysis
by VulDB Data Team • 09/06/2022
The xmlBufAttrSerializeTxtContent function in libxml2 represents a critical vulnerability that demonstrates how improper handling of character encoding during XML serialization can lead to severe system instability. This flaw exists within the xmlsave.c module of the widely-used libxml2 library, which serves as the foundation for XML processing in numerous applications across different operating systems and platforms. The vulnerability specifically manifests when the library encounters non-UTF-8 attribute values during serialization operations, creating a scenario where context-dependent attackers can exploit this weakness to trigger unexpected behavior in affected systems.
The technical implementation of this vulnerability stems from inadequate bounds checking within the xmlBufAttrSerializeTxtContent function, which fails to properly validate or sanitize attribute values before processing them for serialization. When the library encounters attribute content that does not conform to UTF-8 encoding standards, the function attempts to read memory locations beyond the allocated buffer boundaries, resulting in out-of-bounds read operations. This memory access violation directly translates into application crashes and system instability, as the program attempts to access invalid memory addresses during the serialization process. The flaw operates at the intersection of character encoding handling and memory management, making it particularly dangerous in environments where XML processing is prevalent.
The operational impact of CVE-2016-4483 extends beyond simple denial of service, as it can be leveraged by attackers to disrupt services and potentially escalate privileges within affected systems. Applications utilizing libxml2 for XML processing, including web servers, database systems, and enterprise software platforms, become vulnerable to this attack vector when processing user-supplied XML content containing non-UTF-8 attribute values. The vulnerability's context-dependent nature means that exploitation requires specific conditions where the application processes malformed XML data, but once triggered, the consequences can be devastating for system availability and stability. This type of vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and represents a classic example of how character encoding issues can lead to memory safety problems.
The broader implications of this vulnerability highlight the critical importance of proper input validation and encoding handling in security-critical libraries. Given that libxml2 is utilized by numerous applications and frameworks, a single vulnerability in this component can affect a vast ecosystem of software systems. The potential for exploitation increases significantly in web applications where user input directly influences XML processing, as attackers can craft malicious XML payloads designed to trigger this specific memory access violation. Organizations should consider implementing defensive measures such as input sanitization, character encoding normalization, and regular library updates to mitigate the risk. This vulnerability also demonstrates the importance of adhering to ATT&CK framework concepts related to privilege escalation and denial of service, as the exploitation can lead to service disruption and potentially more serious system compromise depending on the application context. The duplicate relationship with CVE-2016-3627 further emphasizes the need for comprehensive vulnerability management and the recognition that similar flaws can exist across different functions within the same library, requiring thorough analysis and remediation approaches.