CVE-2009-0749 in OptiPNG
Summary
by MITRE
Use-after-free vulnerability in the GIFReadNextExtension function in lib/pngxtern/gif/gifread.c in OptiPNG 0.6.2 and earlier allows context-dependent attackers to cause a denial of service (application crash) via a crafted GIF image that causes the realloc function to return a new pointer, which triggers memory corruption when the old pointer is accessed.
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Analysis
by VulDB Data Team • 08/30/2019
The vulnerability described in CVE-2009-0749 represents a classic use-after-free flaw within the OptiPNG image processing library that affects versions 0.6.2 and earlier. This type of vulnerability occurs when a program continues to reference memory after it has been freed, creating opportunities for memory corruption and system instability. The specific function affected is GIFReadNextExtension located in the lib/pngextern/gif/gifread.c file, which handles the parsing of GIF image extensions during the image processing workflow.
The technical mechanism behind this vulnerability involves the realloc function behavior during memory management operations. When the GIF processing code encounters a specially crafted GIF file, the realloc function returns a new memory pointer while the original pointer remains in use elsewhere within the program execution flow. This creates a scenario where subsequent memory access operations target deallocated memory regions, leading to unpredictable behavior and ultimately application crashes. The flaw demonstrates poor memory management practices where the program fails to properly update all references to the relocated memory block after a reallocation event.
From an operational perspective, this vulnerability presents a significant denial of service risk for systems processing GIF images through OptiPNG. Attackers can craft malicious GIF files that trigger the use-after-free condition, causing the application to crash and terminate unexpectedly. This makes the vulnerability particularly dangerous in automated processing environments or web applications that accept user-uploaded GIF files, where a single malicious image could disrupt service availability. The context-dependent nature of the attack means that exploitation requires specific conditions related to the image format and processing workflow, but the impact remains severe enough to warrant immediate attention.
The vulnerability maps directly to CWE-416, which specifically addresses the use of freed memory condition in software development practices. This weakness falls under the broader category of memory safety issues that have plagued software systems for decades, with use-after-free vulnerabilities being among the most common and dangerous classes of memory corruption flaws. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.001, which covers network denial of service attacks through application crashes and resource exhaustion. The vulnerability's exploitation path is straightforward and requires minimal specialized knowledge, making it attractive to threat actors seeking to disrupt services.
Mitigation strategies for this vulnerability should focus on immediate version upgrades to OptiPNG 0.7.0 or later, which contain the necessary fixes for the memory management issues. Additionally, implementing proper input validation and sanitization for GIF image files can help prevent malicious payloads from reaching the vulnerable parsing functions. System administrators should also consider deploying web application firewalls or content filtering solutions that can detect and block suspicious GIF file patterns. Organizations using OptiPNG in automated workflows should implement robust error handling and recovery mechanisms to prevent single-point failures, while also monitoring for unusual application crash patterns that might indicate exploitation attempts. The fix typically involves ensuring that all memory references are properly updated after realloc operations and implementing proper memory lifecycle management practices throughout the image processing pipeline.