CVE-2006-5823 in Linux
Summary
by MITRE
The zlib_inflate function in Linux kernel 2.6.x allows local users to cause a denial of service (crash) via a malformed filesystem that uses zlib compression that triggers memory corruption, as demonstrated using cramfs.
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Analysis
by VulDB Data Team • 04/27/2026
The vulnerability identified as CVE-2006-5823 represents a critical denial of service weakness in the Linux kernel's handling of compressed filesystems. This issue specifically affects the zlib_inflate function within kernel versions 2.6.x, where improper validation of compressed data leads to memory corruption conditions that ultimately result in system crashes. The vulnerability manifests when malformed filesystems utilizing zlib compression are processed, with cramfs serving as the primary demonstration of this weakness. The flaw exploits the kernel's decompression routines without adequate bounds checking or error handling for corrupted compressed data streams.
The technical implementation of this vulnerability stems from insufficient input validation within the kernel's compression handling subsystem. When the zlib_inflate function processes compressed data from filesystems like cramfs, it fails to properly validate the integrity and structure of the compressed data before attempting decompression. This lack of proper validation allows maliciously crafted compressed data to trigger buffer overflows or memory corruption patterns that cause the kernel to crash. The vulnerability operates at the kernel level where memory management and compression algorithms intersect, making it particularly dangerous as it can be exploited by local users without requiring special privileges or network access.
The operational impact of CVE-2006-5823 extends beyond simple system crashes to potentially compromise system availability and stability. Local users can exploit this vulnerability to repeatedly crash the kernel when attempting to access or mount affected filesystems, leading to persistent denial of service conditions that can render systems unusable. The vulnerability affects systems running kernel versions 2.6.x, which were widely deployed across various server and desktop environments at the time of discovery. This widespread adoption meant that numerous systems could be simultaneously vulnerable to exploitation, creating potential for large-scale service disruption.
Mitigation strategies for this vulnerability require immediate kernel updates and patches from vendors to address the flawed decompression logic. System administrators should prioritize applying security patches that include proper bounds checking and memory validation for compressed data streams. Additional protective measures include disabling unnecessary filesystem support, implementing proper filesystem validation before mounting, and monitoring system logs for unusual kernel crash patterns. The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and relates to ATT&CK technique T1499.004 for network denial of service attacks. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across all affected kernel versions.