CVE-2005-1849 in zlib
Summary
by MITRE
inftrees.h in zlib 1.2.2 allows remote attackers to cause a denial of service (application crash) via an invalid file that causes a large dynamic tree to be produced.
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Analysis
by VulDB Data Team • 06/30/2025
The vulnerability described in CVE-2005-1849 represents a critical denial of service weakness within the zlib compression library version 1.2.2. This issue specifically affects the inftrees.h component which handles the decompression of deflate-compressed data streams. The flaw arises when malformed input data is processed by the decompression routine, leading to unpredictable behavior that can result in application crashes and system instability. The vulnerability demonstrates a classic case of insufficient input validation where the compression library fails to properly handle corrupted or maliciously crafted compressed data structures.
The technical root cause of this vulnerability lies in the improper handling of dynamic Huffman trees during the decompression process. When zlib encounters an invalid compressed file, particularly one containing malformed dynamic tree definitions, the decompression algorithm can enter an infinite loop or allocate excessive memory resources. This occurs because the library does not adequately validate the structure and bounds of dynamic tree definitions before processing them. The flaw falls under CWE-129 which specifically addresses improper validation of array indices and buffer overflows, while also relating to CWE-770 which covers insufficient resource management and excessive resource consumption. The vulnerability enables attackers to exploit the decompression logic through crafted compressed data that triggers resource exhaustion or algorithmic complexity issues.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise entire systems that rely on zlib for data compression. Applications that process untrusted compressed data, including web servers, file processing utilities, and network protocols that utilize deflate compression, become vulnerable to this attack vector. When exploited, the vulnerability can cause applications to consume excessive CPU cycles or memory resources, leading to system instability, application crashes, or complete service unavailability. This type of denial of service attack can be particularly dangerous in environments where compressed data is processed automatically without proper validation, as it can be triggered through normal user interactions or automated processing pipelines.
Mitigation strategies for CVE-2005-1849 should focus on both immediate patching and defensive programming practices. The most effective solution involves upgrading to zlib version 1.2.3 or later, which includes proper bounds checking and input validation for dynamic tree structures. Organizations should implement comprehensive input validation procedures for all compressed data processing, including the use of strict compression format validation before decompression operations. Additionally, system administrators should consider implementing resource limits and timeouts for decompression operations to prevent exploitation from consuming excessive system resources. The ATT&CK framework categorizes this vulnerability under T1499 which covers network denial of service attacks, and T1210 which addresses exploitation of vulnerabilities in software libraries. Implementing proper error handling and recovery mechanisms within applications that use zlib can also help prevent exploitation of this vulnerability. Organizations should also consider deploying intrusion detection systems that can identify suspicious patterns in compressed data processing that may indicate attempted exploitation of this or similar vulnerabilities.