CVE-2006-5726 in FreeBSD
Summary
by MITRE
alloccgblk in the UFS filesystem in Solaris 10 allows local users to cause a denial of service (memory corruption) by mounting crafted UFS filesystems with malformed data structures.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability identified as CVE-2006-5726 resides within the alloccgblk function of the Universal File System implementation in Solaris 10 operating systems. This flaw represents a critical memory corruption issue that manifests when local users attempt to mount specially crafted UFS filesystems containing malformed data structures. The vulnerability operates at the kernel level within the file system subsystem, specifically targeting the cluster group allocation mechanism that manages storage blocks in UFS filesystems.
The technical root cause of this vulnerability stems from inadequate input validation within the alloccgblk function which processes cluster group allocations during filesystem mounting operations. When malformed data structures are encountered during the mounting process, the function fails to properly validate the integrity of the UFS metadata, leading to memory corruption patterns that can result in system instability or complete system crashes. This represents a classic buffer over-read or improper memory handling vulnerability that falls under the CWE-125 weakness category for out-of-bounds read conditions. The flaw specifically affects the UFS filesystem's ability to properly parse and validate cluster group information, causing the kernel to attempt operations on invalid memory locations.
From an operational perspective, this vulnerability presents a significant denial of service risk that can be exploited by local users with minimal privileges. The impact extends beyond simple service disruption as memory corruption can potentially lead to system crashes, data loss, or in severe cases, system compromise. The vulnerability is particularly concerning because it can be triggered through the standard filesystem mounting mechanism, meaning any local user with the ability to mount filesystems can potentially exploit this weakness. The attack vector requires only that an attacker can create or access a crafted UFS filesystem image, making this vulnerability accessible in numerous scenarios including removable media attacks, network file sharing, or compromised system components.
The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for Network Denial of Service, though it operates at a lower privilege level since it requires local access. The vulnerability's exploitation pattern aligns with privilege escalation techniques and can serve as a foundation for more complex attacks if combined with other weaknesses. Security professionals should note that this vulnerability demonstrates the critical importance of proper input validation in kernel-level code and highlights the potential for seemingly benign file system operations to result in system-wide failures. The vulnerability also underscores the need for comprehensive testing of file system parsers against malformed inputs and proper memory management practices in operating system kernels.
Mitigation strategies for this vulnerability include immediate application of Oracle's security patches and updates for Solaris 10 systems, particularly those addressing UFS filesystem handling and memory management. System administrators should implement strict access controls to prevent unauthorized users from mounting arbitrary filesystems, though this is not a complete defense since local users with sufficient privileges can still exploit the vulnerability. The recommended approach involves monitoring filesystem mounting operations and implementing proper input sanitization procedures. Additionally, organizations should conduct regular vulnerability assessments to identify similar weaknesses in other filesystem implementations and ensure that kernel-level code follows established security practices. The vulnerability serves as a reminder of the critical need for robust input validation in all system components and the importance of maintaining up-to-date security patches across all operating system versions.