CVE-2011-2896 in CUPS
Summary
by MITRE
The LZW decompressor in the LWZReadByte function in giftoppm.c in the David Koblas GIF decoder in PBMPLUS, as used in the gif_read_lzw function in filter/image-gif.c in CUPS before 1.4.7, the LZWReadByte function in plug-ins/common/file-gif-load.c in GIMP 2.6.11 and earlier, the LZWReadByte function in img/gifread.c in XPCE in SWI-Prolog 5.10.4 and earlier, and other products, does not properly handle code words that are absent from the decompression table when encountered, which allows remote attackers to trigger an infinite loop or a heap-based buffer overflow, and possibly execute arbitrary code, via a crafted compressed stream, a related issue to CVE-2006-1168 and CVE-2011-2895.
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Analysis
by VulDB Data Team • 11/18/2021
The vulnerability described in CVE-2011-2896 represents a critical flaw in LZW decompression implementations across multiple image processing libraries and applications. This issue affects the fundamental decompression logic used in GIF image handling, where the LZWReadByte function fails to properly validate code words during decompression. The flaw occurs when encountering code words that are absent from the decompression table, creating a condition that can lead to either infinite loops or heap-based buffer overflows. The vulnerability impacts widely used software components including CUPS print system versions prior to 1.4.7, GIMP image editor versions up to 2.6.11, and SWI-Prolog versions up to 5.10.4, making it particularly dangerous due to its widespread presence in various computing environments.
The technical nature of this vulnerability stems from improper handling of the LZW decompression algorithm's table management during the decompression process. When the decompressor encounters a code word that should have been present in the decompression table but is actually missing, the implementation fails to properly validate this condition. This missing validation creates a path where the decompression routine can enter an infinite loop when processing malformed input data, or alternatively trigger a heap-based buffer overflow when attempting to write beyond allocated memory boundaries. The flaw is particularly insidious because it can be exploited through crafted GIF files that contain malformed LZW compression data, making it a classic example of a denial-of-service vulnerability that can potentially be escalated to arbitrary code execution.
The operational impact of CVE-2011-2896 extends far beyond simple service disruption, as it affects core image processing functionality across multiple software domains. In the context of print management systems like CUPS, exploitation could allow attackers to cause print servers to consume excessive resources or crash entirely, disrupting document processing workflows. For image editing applications such as GIMP, the vulnerability could enable remote code execution when users open maliciously crafted GIF files, potentially compromising entire workstations. The attack surface is significantly broadened by the fact that the vulnerability exists in multiple implementations of the same core algorithm, meaning that exploitation techniques developed for one affected application could potentially be adapted for others. This vulnerability aligns with CWE-129, which describes improper validation of input boundaries, and represents a classic example of how decompression algorithms can be exploited when proper bounds checking is not implemented.
From an adversarial perspective, this vulnerability fits squarely within the ATT&CK framework under the T1203 technique for "Exploitation for Execution" and T1059 for "Command and Scripting Interpreter" as attackers could leverage the heap overflow to execute arbitrary code. The vulnerability is particularly concerning because it requires no special privileges to exploit, making it suitable for user-level attacks against applications that process untrusted image data. The related CVE-2006-1168 and CVE-2011-2895 indicate that this represents a recurring pattern of LZW decompression flaws in image processing libraries, suggesting that similar vulnerabilities may exist in other decompression implementations. Organizations should prioritize patching affected systems, implementing input validation for image files, and deploying network segmentation to limit potential exploitation opportunities, particularly in environments where untrusted image files may be processed automatically.
The remediation approach for CVE-2011-2896 requires immediate attention to patched versions of affected software, with particular emphasis on updating CUPS to version 1.4.7 or later, GIMP to version 2.6.12 or later, and SWI-Prolog to version 5.10.5 or later. Additionally, administrators should implement strict input validation for GIF files, particularly in web applications and file processing systems that handle user-uploaded content. The vulnerability demonstrates the importance of robust error handling in compression algorithms and highlights the need for comprehensive testing of edge cases in decompression routines. Security teams should also consider implementing automated scanning for vulnerable libraries and establishing monitoring for unusual resource consumption patterns that might indicate exploitation attempts.