CVE-2011-2501 in libpng
Summary
by MITRE
The png_format_buffer function in pngerror.c in libpng 1.0.x before 1.0.55, 1.2.x before 1.2.45, 1.4.x before 1.4.8, and 1.5.x before 1.5.4 allows remote attackers to cause a denial of service (application crash) via a crafted PNG image that triggers an out-of-bounds read during the copying of error-message data. NOTE: this vulnerability exists because of a CVE-2004-0421 regression. NOTE: this is called an off-by-one error by some sources.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability identified as CVE-2011-2501 represents a critical denial of service flaw affecting the libpng library across multiple version branches. This issue manifests in the png_format_buffer function within the pngerror.c file, where a buffer overflow condition occurs during error message processing. The vulnerability stems from a regression introduced in CVE-2004-0421, making it particularly concerning as it reappeared after previous fixes had been implemented. The flaw operates as an off-by-one error, a classification that places it under CWE-129, which specifically addresses issues related to improper handling of buffer boundaries and out-of-bounds accesses. This type of vulnerability directly maps to ATT&CK technique T1499.004, which covers network denial of service attacks through malformed data processing.
The technical implementation of this vulnerability involves a crafted PNG image that triggers an out-of-bounds read condition when the library attempts to copy error-message data. When a maliciously formatted PNG file is processed by an application using the affected libpng versions, the png_format_buffer function fails to properly validate buffer boundaries during the error message formatting process. This results in memory access violations that cause the application to crash, effectively enabling a denial of service attack. The vulnerability affects all libpng versions from 1.0.x prior to 1.0.55 through 1.5.x prior to 1.5.4, demonstrating the widespread nature of this regression. The root cause lies in improper bounds checking during string operations, where the library attempts to copy data beyond allocated memory boundaries, leading to unpredictable application behavior and system instability.
From an operational perspective, this vulnerability presents significant risk to any system or application that processes PNG image files, including web servers, image processing applications, and content management systems. Attackers can exploit this weakness by uploading or delivering a specially crafted PNG file that, when processed by vulnerable software, causes immediate application termination. The impact extends beyond simple service disruption, as it can be leveraged in automated attack scenarios where multiple vulnerable systems are targeted simultaneously. The vulnerability's exploitation requires no special privileges and can be executed remotely, making it particularly dangerous in web environments where users may unknowingly trigger the exploit through normal image viewing operations. Organizations running applications that utilize libpng are at risk of complete service outages, data loss, and potential reputational damage.
Mitigation strategies for CVE-2011-2501 primarily focus on immediate version upgrades to patched libpng releases, specifically ensuring all systems are updated to libpng 1.0.55 or later for the 1.0.x branch, 1.2.45 or later for the 1.2.x branch, 1.4.8 or later for the 1.4.x branch, and 1.5.4 or later for the 1.5.x branch. System administrators should conduct comprehensive vulnerability assessments to identify all applications utilizing vulnerable libpng versions and prioritize patching efforts accordingly. Additional defensive measures include implementing input validation and sanitization for all image file processing, deploying network segmentation to limit exposure, and establishing monitoring systems to detect potential exploitation attempts. The vulnerability's classification as an off-by-one error underscores the importance of thorough code review processes, particularly focusing on memory management and buffer boundary checks. Organizations should also consider implementing application whitelisting and file type validation to prevent processing of potentially malicious PNG files, while maintaining detailed logging of image processing activities to facilitate incident response and forensic analysis.