CVE-2016-9842 in tvOS
Summary
by MITRE
The inflateMark function in inflate.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact via vectors involving left shifts of negative integers.
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Analysis
by VulDB Data Team • 07/14/2026
The vulnerability identified as CVE-2016-9842 resides within the inflateMark function of the zlib compression library version 1.2.8. This flaw manifests in the handling of integer operations during decompression processes, specifically when dealing with left shift operations on negative integers. The issue represents a classic example of undefined behavior in C programming languages where operations on signed integers can produce unpredictable results depending on the underlying implementation and system architecture. The vulnerability falls under the category of implementation flaws that can lead to various security implications including potential denial of service or information disclosure.
The technical root cause of this vulnerability stems from how the inflateMark function processes compressed data streams that may contain malformed or maliciously crafted inputs. When the function performs left shifts on negative integer values, the behavior becomes implementation-defined according to the c standard, meaning different compilers or architectures may handle such operations differently. This creates opportunities for attackers to craft specific input sequences that can trigger unexpected execution paths within the decompression logic. The vulnerability is context-dependent because it requires specific conditions to be met during the decompression process, typically involving particular patterns in compressed data that cause the function to process negative values in shift operations.
From an operational impact perspective, this vulnerability can lead to several serious consequences depending on how zlib is utilized within applications. When exploited, the vulnerability may cause applications using zlib to crash or behave unpredictably, resulting in denial of service conditions. In some scenarios, particularly when the vulnerability occurs in memory management contexts, it could potentially be leveraged to disclose sensitive information from memory or even execute arbitrary code. The attack vector requires that an application using zlib processes maliciously crafted compressed data, making it particularly relevant in web applications, file processing systems, and network protocols that rely on compression. This vulnerability demonstrates the critical importance of proper input validation and robust error handling in cryptographic and compression libraries that are widely used throughout the software ecosystem.
Mitigation strategies for CVE-2016-9842 primarily focus on updating to patched versions of zlib where the issue has been resolved through proper handling of integer operations and elimination of the problematic left shift operations on negative values. System administrators and developers should prioritize upgrading to zlib version 1.2.9 or later, which contains the necessary fixes. Additionally, implementing input validation measures and sanitization of compressed data before processing can provide defense-in-depth protection. The vulnerability aligns with CWE-755 weakness category related to improper handling of exceptional conditions and can be mapped to ATT&CK technique T1059.007 for command and scripting interpreter, particularly when considering potential exploitation paths through application-level attacks. Organizations should also implement monitoring and logging mechanisms to detect unusual decompression activities that might indicate exploitation attempts, as the vulnerability can be particularly subtle and difficult to detect through standard security scanning tools.