CVE-2005-2456 in Linux
Summary
by MITRE
Array index overflow in the xfrm_sk_policy_insert function in xfrm_user.c in Linux kernel 2.6 allows local users to cause a denial of service (oops or deadlock) and possibly execute arbitrary code via a p->dir value that is larger than XFRM_POLICY_OUT, which is used as an index in the sock->sk_policy array.
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Analysis
by VulDB Data Team • 09/05/2019
The vulnerability described in CVE-2005-2456 represents a critical array index overflow condition within the Linux kernel's IPsec implementation, specifically in the xfrm_user.c file. This flaw exists in kernel versions 2.6 and affects the xfrm_sk_policy_insert function which handles policy insertion for IPsec security associations. The vulnerability stems from inadequate bounds checking when processing the p->dir value parameter, which serves as an index into the sock->sk_policy array structure. When this value exceeds the legitimate XFRM_POLICY_OUT boundary, the function fails to validate the index range, creating a potential for memory corruption and system instability.
The technical implementation of this vulnerability occurs within the kernel's security policy management subsystem where IPsec policies are stored and managed for network traffic. The sock->sk_policy array is designed to hold multiple policy entries indexed by direction values, with XFRM_POLICY_OUT representing the maximum valid index for outbound policies. However, the absence of proper validation allows attackers to specify an index value that exceeds this boundary, resulting in an array index overflow. This condition can manifest as either a kernel oops (a type of kernel panic) or a deadlock situation that effectively renders the system unusable. The overflow can potentially overwrite adjacent memory locations, creating opportunities for privilege escalation and arbitrary code execution.
From an operational perspective, this vulnerability presents a significant risk to systems running affected kernel versions as local users can exploit it to cause system denial of service or potentially gain elevated privileges. The attack vector requires local access to the system, making it less immediately dangerous than remote exploits but still highly concerning for environments where untrusted users might have shell access. The vulnerability can be particularly problematic in multi-user environments where privilege separation is not strictly enforced. The impact extends beyond simple denial of service to potentially allow for privilege escalation, as memory corruption can be leveraged to execute malicious code within kernel space. This aligns with ATT&CK technique T1068 which covers 'Exploitation for Privilege Escalation' and CWE-129 which addresses 'Improper Validation of Array Index' as the underlying weakness.
Mitigation strategies for this vulnerability involve immediate kernel updates to patched versions that implement proper bounds checking for the policy direction index values. The fix typically involves adding validation logic to ensure that p->dir values remain within the legitimate range of 0 to XFRM_POLICY_OUT, preventing the overflow condition from occurring. System administrators should also implement monitoring for unusual kernel oops messages or system lockups that might indicate exploitation attempts. Additional defensive measures include restricting local user privileges where possible, implementing proper access controls for system resources, and maintaining up-to-date security patches across all kernel versions in use. The vulnerability demonstrates the importance of proper input validation in kernel space code and highlights the critical nature of memory safety mechanisms in operating system components. Organizations should prioritize patch management processes to ensure rapid deployment of security fixes and maintain comprehensive inventory of kernel versions across their infrastructure to prevent exploitation of similar vulnerabilities in the future.