CVE-2008-1940 in Kernel Patch
Summary
by MITRE
The RBAC functionality in grsecurity before 2.1.11-2.6.24.5 and 2.1.11-2.4.36.2 does not enforce user_transition_deny and user_transition_allow rules for the (1) sys_setfsuid and (2) sys_setfsgid calls, which allows local users to bypass restrictions for those calls.
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Analysis
by VulDB Data Team • 11/12/2017
The vulnerability identified as CVE-2008-1940 resides within the grsecurity kernel security module, specifically targeting the Role-Based Access Control implementation that was present in versions prior to 2.1.11-2.6.24.5 and 2.1.11-2.4.36.2. This flaw represents a critical weakness in the kernel's privilege management system where the mandatory access control policies fail to properly enforce user transition rules for specific system calls. The affected system calls are sys_setfsuid and sys_setfsgid which are responsible for setting the filesystem user and group IDs respectively. These calls are fundamental to Unix-like operating systems and are commonly utilized by processes requiring elevated privileges to perform file system operations.
The technical implementation flaw stems from the incomplete enforcement of user_transition_deny and user_transition_allow rules within the grsecurity RBAC framework. These rules are designed to control which users or processes can transition to specific user contexts when executing privileged operations. The vulnerability manifests when the kernel fails to validate these transition rules against the sys_setfsuid and sys_setfsgid system calls, allowing local attackers to bypass the intended access controls. This represents a direct violation of the principle of least privilege and undermines the entire security model that grsecurity attempts to enforce. The flaw is classified under CWE-284 Access Control, specifically dealing with insufficient access control mechanisms and improper enforcement of access control policies.
The operational impact of this vulnerability is significant for systems utilizing grsecurity as their primary kernel security solution. Local users who can execute processes on the affected systems gain the ability to escalate their privileges without proper authorization, effectively bypassing the security controls that should prevent unauthorized transitions between user contexts. This weakness can be exploited to gain elevated privileges, potentially leading to full system compromise. Attackers can leverage this vulnerability to circumvent security boundaries that were intended to prevent unauthorized access to resources, making it particularly dangerous in multi-user environments or systems where privilege separation is critical. The vulnerability affects the core functionality of grsecurity's access control policies and can be exploited to undermine the integrity and confidentiality of the system.
Mitigation strategies for this vulnerability require immediate patching of the grsecurity kernel module to versions 2.1.11-2.6.24.5 and 2.1.11-2.4.36.2 or later, which contain the necessary fixes to properly enforce user transition rules for the affected system calls. System administrators should also implement additional monitoring and logging of setfsuid and setfsgid operations to detect potential exploitation attempts. The remediation aligns with ATT&CK technique T1068, which involves exploiting local privilege escalation vulnerabilities, and T1548.001, which covers abuse of privilege escalation techniques. Organizations should conduct thorough security assessments to ensure that all systems running grsecurity are updated and that proper access control policies are in place. Additionally, implementing process monitoring and intrusion detection systems can help identify anomalous behavior that might indicate exploitation attempts, particularly around filesystem user and group ID changes. The vulnerability demonstrates the critical importance of comprehensive testing and validation of access control mechanisms, especially in security modules that operate at the kernel level where flaws can have widespread system implications.