CVE-2008-5907 in libpng
Summary
by MITRE
The png_check_keyword function in pngwutil.c in libpng before 1.0.42, and 1.2.x before 1.2.34, might allow context-dependent attackers to set the value of an arbitrary memory location to zero via vectors involving creation of crafted PNG files with keywords, related to an implicit cast of the \0 character constant to a NULL pointer. NOTE: some sources incorrectly report this as a double free vulnerability.
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Analysis
by VulDB Data Team • 06/08/2025
The vulnerability described in CVE-2008-5907 represents a critical memory corruption issue within the libpng library, specifically affecting versions prior to 1.0.42 and 1.2.34. This flaw exists in the png_check_keyword function located in the pngwutil.c file, which handles keyword validation during PNG file processing. The vulnerability stems from an implicit type conversion that occurs when handling character constants, creating a dangerous condition where attacker-controlled data can manipulate memory addresses through crafted PNG files. The issue manifests when the library processes specially constructed PNG keywords that trigger an implicit cast of a character constant to a NULL pointer, enabling attackers to manipulate memory locations in ways that could lead to arbitrary code execution or system compromise.
The technical exploitation of this vulnerability relies on the improper handling of keyword strings during PNG file parsing, where the implicit cast of character constants creates a scenario that allows attackers to manipulate memory pointers. This flaw specifically targets the memory management operations within libpng's keyword validation logic, where the function fails to properly validate or sanitize input data before processing. The vulnerability's context-dependent nature means that exploitation requires specific conditions, including the ability to create and process crafted PNG files that contain malicious keyword data. The implicit cast behavior creates a path where a null pointer dereference can occur, potentially allowing attackers to set arbitrary memory locations to zero, which represents a form of memory corruption that can be leveraged for more severe attacks including privilege escalation or denial of service conditions.
The operational impact of this vulnerability extends across numerous systems that utilize libpng for image processing, including web servers, desktop applications, and network services that handle PNG file uploads or processing. Systems running vulnerable versions of libpng are susceptible to remote code execution when processing maliciously crafted PNG files, as demonstrated by the potential for attackers to manipulate memory locations and potentially execute arbitrary code. This vulnerability affects not only web applications but also any software that depends on libpng for image handling, including content management systems, image processing applications, and network appliances that process PNG files. The risk is particularly high in environments where users can upload or submit PNG files, as this creates an attack surface where malicious actors can exploit the vulnerability to compromise system integrity and potentially gain unauthorized access to sensitive data or system resources.
Mitigation strategies for CVE-2008-5907 primarily focus on upgrading to patched versions of libpng, specifically versions 1.0.42 or later for the 1.0.x branch and 1.2.34 or later for the 1.2.x branch. Organizations should implement comprehensive patch management procedures to ensure all systems utilizing libpng are updated promptly. Additional defensive measures include implementing strict input validation for PNG file processing, deploying web application firewalls to filter malicious file uploads, and establishing monitoring systems to detect unusual file processing patterns. The vulnerability aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to ATT&CK technique T1059 for execution through command injection, though the specific vector here involves memory corruption rather than direct code execution. System administrators should also consider implementing sandboxing mechanisms for image processing operations and conducting regular security assessments to identify potential exposure points in their PNG handling infrastructure.