CVE-2017-16794 in SWFTools
Summary
by MITRE
The png_load function in lib/png.c in SWFTools 0.9.2 does not properly validate a multiplication of width and bits-per-pixel values, which allows remote attackers to cause a denial of service (heap-based buffer over-read and application crash) via a crafted file, as demonstrated by an erroneous png_load call that occurs because of incorrect integer data types in png2swf.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-16794 resides within the SWFTools 0.9.2 software suite, specifically within the png_load function located in lib/png.c. This flaw represents a classic integer overflow condition that occurs during the processing of portable network graphics files. The vulnerability manifests when the software attempts to calculate buffer sizes for heap allocation by multiplying the width value with bits-per-pixel values without proper validation of the resulting product. This mathematical operation fails to account for potential integer overflow scenarios that could occur when dealing with large image dimensions or high bit-depth values, creating a scenario where the calculated buffer size becomes insufficient for the actual data requirements.
The technical exploitation of this vulnerability involves a remote attacker crafting a malicious png file with carefully constructed dimensions and bit-depth parameters that, when processed by png2swf, trigger the improper multiplication calculation. The flaw stems from inadequate input validation mechanisms that should have verified whether the multiplication result would exceed the maximum representable value for the target data type. This issue falls under the CWE-190 category of integer overflow and under the broader category of CWE-129 input validation failures. The vulnerability is particularly dangerous because it operates at the heap memory level, where the buffer over-read condition can lead to arbitrary code execution or complete application crash, making it a prime candidate for denial of service attacks that can be remotely triggered.
From an operational perspective, this vulnerability affects any system running SWFTools 0.9.2 that processes untrusted png files through the png2swf utility. The impact extends beyond simple service disruption as the heap-based buffer over-read can potentially lead to memory corruption that may be exploited for more sophisticated attacks. The vulnerability demonstrates a failure in proper integer arithmetic handling that is commonly seen in legacy software systems where modern security practices were not fully implemented. Attackers can leverage this weakness by uploading or transmitting specially crafted png files that cause the application to allocate insufficient memory buffers, leading to memory corruption and application instability.
The mitigation strategies for this vulnerability require immediate software updates to versions that address the integer overflow condition through proper validation of multiplication results before buffer allocation. System administrators should implement input validation measures that restrict file dimensions and bit-depth values to reasonable limits that prevent overflow conditions. Additionally, deploying network segmentation and access controls can limit exposure by restricting access to systems processing untrusted graphics files. The vulnerability highlights the importance of implementing proper integer overflow protections as outlined in the software security guidelines and represents a typical scenario where the ATT&CK framework would classify this under the T1499 technique of network denial of service. Organizations should also consider implementing automated file validation systems that can detect and quarantine suspicious file characteristics before they reach the vulnerable processing functions. The remediation process should include comprehensive testing of updated software versions to ensure that the integer overflow protection mechanisms function correctly and that no similar vulnerabilities exist in related code components.