CVE-2017-6960 in apng2gif
Summary
by MITRE • 01/25/2023
An issue was discovered in apng2gif 1.7. There is an integer overflow resulting in a heap-based buffer over-read, related to the load_apng function and the imagesize variable.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2017-6960 resides within the apng2gif utility version 1.7, a tool designed to convert animated png files to gif format. This flaw manifests as an integer overflow condition that ultimately leads to a heap-based buffer over-read, representing a critical security weakness in the software's handling of animated png image data. The vulnerability specifically affects the load_apng function which processes animated png files and utilizes an imagesize variable that becomes susceptible to overflow conditions during memory allocation calculations. The integer overflow occurs when the application attempts to compute memory requirements for processing animated png frames, where the calculation fails to properly validate input parameters and can result in insufficient memory allocation for the intended buffer size. This condition creates a scenario where the application attempts to read from memory locations beyond the allocated buffer boundaries, potentially exposing sensitive data or allowing arbitrary code execution.
The technical implementation of this vulnerability follows a well-established pattern of integer overflow leading to memory corruption issues. When the load_apng function processes an animated png file, it calculates the total image size required for storage by multiplying various dimensions and frame counts. If these calculations exceed the maximum value that can be represented by the integer type used for the imagesize variable, the overflow occurs and results in a negative or unexpectedly large value. This miscalculated value then gets used to allocate heap memory, creating a buffer that is significantly smaller than required. Subsequent memory reads beyond this artificially constrained buffer cause the over-read condition, which can be exploited by malicious actors to access adjacent memory regions or potentially overwrite critical program data structures.
From an operational perspective, this vulnerability poses significant risks to systems that process animated png files through the apng2gif utility, particularly in environments where untrusted input is accepted. The heap-based buffer over-read can lead to information disclosure, application crashes, or in more severe cases, arbitrary code execution depending on the memory layout and exploitation circumstances. Attackers could craft specially malformed animated png files that trigger the integer overflow condition, potentially leading to privilege escalation or complete system compromise if the utility runs with elevated permissions. The vulnerability is particularly concerning because it operates within a conversion utility that might be used in automated processing pipelines, web applications, or content management systems where such files are frequently handled. The exploitability of this issue is enhanced by the fact that animated png files are commonly used on the web and in various digital media applications, making the attack surface quite broad.
Security mitigations for CVE-2017-6960 should focus on immediate patching of the apng2gif utility to version 1.8 or later, which contains the necessary fixes for the integer overflow condition. The fix typically involves implementing proper input validation and boundary checking for the imagesize variable calculation, ensuring that integer overflows are detected and handled gracefully before memory allocation occurs. Additionally, system administrators should implement input sanitization measures for any applications that process animated png files, including limiting file size, validating image dimensions, and implementing strict parsing routines that prevent malformed data from reaching vulnerable code paths. The vulnerability aligns with CWE-190, which describes integer overflow conditions, and may map to ATT&CK techniques involving code injection and privilege escalation through memory corruption exploits. Organizations should also consider implementing application whitelisting controls and network segmentation to limit the potential impact of successful exploitation attempts, particularly in environments where the vulnerable utility might be accessible to untrusted users or automated processing systems.