CVE-2008-6218 in libpng
Summary
by MITRE
Memory leak in the png_handle_tEXt function in pngrutil.c in libpng before 1.2.33 rc02 and 1.4.0 beta36 allows context-dependent attackers to cause a denial of service (memory exhaustion) via a crafted PNG file.
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Analysis
by VulDB Data Team • 06/08/2025
The vulnerability identified as CVE-2008-6218 represents a critical memory management flaw within the libpng library implementation that affects versions prior to 1.2.33 rc02 and 1.4.0 beta36. This issue resides in the png_handle_tEXt function located within the pngrutil.c source file, which is responsible for processing text chunks in Portable Network Graphics format files. The flaw manifests as a memory leak that occurs when the library processes specially crafted PNG files containing maliciously constructed tEXt chunks, leading to progressive memory consumption that can ultimately result in system resource exhaustion.
The technical implementation of this vulnerability stems from improper memory deallocation within the png_handle_tEXt function where allocated memory blocks are not correctly freed during the processing of text metadata within PNG files. When an attacker crafts a PNG file with malformed or excessively large tEXt chunks, the libpng library fails to properly manage memory allocation and deallocation cycles, causing memory leaks to accumulate over time. This memory leak behavior creates a condition where each processed malicious PNG file consumes additional memory without proper cleanup, eventually leading to memory exhaustion that can crash applications or render systems unresponsive.
From an operational impact perspective, this vulnerability poses significant risks to systems that process PNG files from untrusted sources, including web applications, image processing servers, and content management systems. The context-dependent nature of the attack means that exploitation requires an attacker to provide a crafted PNG file to a vulnerable application, making it particularly dangerous in environments where users can upload or download image files. The denial of service condition can affect not only individual applications but potentially entire service availability, as memory exhaustion can cause cascading failures in systems that rely on proper PNG processing functionality. This vulnerability directly aligns with CWE-401, which describes improper management of dynamic memory allocation, and can be categorized under ATT&CK technique T1499.004 for network denial of service attacks.
The remediation strategy for CVE-2008-6218 involves upgrading to libpng versions 1.2.33 rc02 or later, or 1.4.0 beta36 and subsequent releases where the memory leak has been properly addressed. System administrators should prioritize patching affected applications that utilize libpng libraries, particularly those handling user-uploaded content or processing external image files. Additionally, implementing input validation and sanitization measures for PNG file processing can provide additional defense-in-depth layers. Organizations should also consider monitoring for unusual memory consumption patterns in applications that process PNG files, as this can serve as an early indicator of potential exploitation attempts. The fix implemented in affected versions typically involves ensuring proper memory deallocation in the png_handle_tEXt function and related text chunk processing routines, preventing the accumulation of leaked memory blocks during normal operation.