CVE-2016-9841 in tvOS
Summary
by MITRE
inffast.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact by leveraging improper pointer arithmetic.
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Analysis
by VulDB Data Team • 07/14/2026
The vulnerability identified as CVE-2016-9841 resides within the inffast.c component of zlib version 1.2.8, representing a critical flaw in the decompression functionality that could be exploited by context-dependent attackers to achieve unspecified but potentially severe consequences. This issue specifically stems from improper pointer arithmetic implementation within the inflate fast decompression routine, which forms a core part of the zlib compression library used extensively across numerous applications and systems worldwide. The flaw manifests when the decompression process handles certain malformed compressed data streams, creating opportunities for attackers to manipulate memory access patterns through carefully crafted inputs that exploit the flawed pointer calculations.
The technical root cause of this vulnerability can be categorized under CWE-128 as "Wrap or Overflow" and more specifically relates to improper pointer arithmetic that occurs during the fast inflate decompression algorithm. When zlib processes compressed data using the inffast.c implementation, it employs pointer arithmetic to navigate through the decompressed output buffer and input data streams. The vulnerability arises when the arithmetic operations used to calculate buffer positions become invalid due to improper handling of certain bit patterns or data sequences that cause pointer values to exceed valid memory boundaries. This improper arithmetic can result in memory corruption, where the decompression routine attempts to write data beyond allocated buffer limits or read from invalid memory locations, potentially leading to arbitrary code execution or denial of service conditions.
The operational impact of CVE-2016-9841 extends far beyond a simple local security issue, as zlib serves as a fundamental compression library used by thousands of applications including web servers, network equipment, operating systems, and various network protocols. Attackers can leverage this vulnerability by crafting malicious compressed data streams that, when processed by affected systems, trigger the faulty pointer arithmetic and potentially execute arbitrary code with the privileges of the affected application. This makes the vulnerability particularly dangerous in web server environments where decompression occurs during HTTP request processing, or in network devices that handle compressed data from various sources. The unspecified impact mentioned in the CVE description reflects the potential for multiple outcomes including remote code execution, information disclosure, or system crashes, depending on the specific exploitation context and target system configuration.
Mitigation strategies for this vulnerability require immediate patching of affected zlib installations to version 1.2.9 or later, which contains the necessary fixes for the pointer arithmetic issues in inffast.c. Organizations should conduct comprehensive inventory assessments to identify all systems using vulnerable zlib versions and prioritize patching efforts accordingly. Network administrators should implement monitoring solutions to detect potential exploitation attempts through unusual decompression patterns or malformed compressed data traffic. The ATT&CK framework categorizes this type of vulnerability under T1059.007 for "Command and Scripting Interpreter: Python" and T1203 for "Exploitation for Client Execution" when considering how attackers might leverage such decompression flaws in broader attack chains. Additionally, defensive measures including input validation for compressed data, rate limiting of decompression operations, and implementation of memory protection mechanisms can help reduce the attack surface and limit the potential impact of successful exploitation attempts.