CVE-2012-6536 in Linux
Summary
by MITRE
net/xfrm/xfrm_user.c in the Linux kernel before 3.6 does not verify that the actual Netlink message length is consistent with a certain header field, which allows local users to obtain sensitive information from kernel heap memory by leveraging the CAP_NET_ADMIN capability and providing a (1) new or (2) updated state.
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Analysis
by VulDB Data Team • 01/01/2022
The vulnerability identified as CVE-2012-6536 resides within the Linux kernel's implementation of the IPsec framework, specifically in the net/xfrm/xfrm_user.c file. This flaw represents a classic buffer over-read condition that occurs when processing Netlink messages through the XFRM (eXtensible Frame Routing Manager) subsystem. The vulnerability manifests when the kernel fails to properly validate the consistency between the actual message length and the length field specified in the Netlink header structure, creating a potential information disclosure scenario that can be exploited by locally privileged attackers.
The technical implementation of this vulnerability stems from insufficient input validation within the kernel's XFRM user interface handling code. When a process with CAP_NET_ADMIN capability attempts to create or modify an IPsec state through the Netlink interface, the kernel's message parsing routine does not adequately verify that the message length field in the Netlink header matches the actual data payload. This inconsistency allows an attacker to craft malicious Netlink messages that can cause the kernel to read beyond the intended buffer boundaries, potentially exposing sensitive data from kernel heap memory. The vulnerability specifically affects Linux kernel versions prior to 3.6, indicating that this was a well-known issue that required kernel-level patching to address the fundamental flaw in message length validation.
Operationally, this vulnerability presents a significant risk to systems running affected kernel versions, particularly those that grant CAP_NET_ADMIN capabilities to processes or users. The attack requires local access with elevated privileges, as the CAP_NET_ADMIN capability is necessary to interact with the XFRM subsystem. However, the impact extends beyond simple privilege escalation, as the information disclosure can potentially expose kernel memory contents including cryptographic keys, session data, or other sensitive operational details that could be leveraged in subsequent attacks. The vulnerability's exploitation potential aligns with the ATT&CK technique T1068, which covers 'Local Privilege Escalation' and 'Credential Access', as it can be used to extract sensitive information that might reveal system configuration details or authentication tokens. From a CWE perspective, this vulnerability maps to CWE-129, which covers 'Improper Validation of Array Index', and CWE-125, which addresses 'Out-of-bounds Read', as the kernel's failure to validate message length creates conditions for reading beyond allocated memory boundaries.
Mitigation strategies for CVE-2012-6536 primarily focus on kernel version updates and access control measures. The most effective solution involves upgrading to Linux kernel version 3.6 or later, where the vulnerability has been addressed through proper message length validation in the XFRM subsystem. Organizations should also implement strict access controls to limit the number of processes or users with CAP_NET_ADMIN capability, as reducing the attack surface significantly minimizes exploitation risk. Additionally, system administrators should monitor for unauthorized processes attempting to interact with the XFRM subsystem and implement logging mechanisms to detect potential exploitation attempts. The vulnerability's remediation also highlights the importance of proper input validation in kernel space code and demonstrates how seemingly minor validation flaws can lead to significant information disclosure risks. Network segmentation and privilege separation practices should be reinforced to ensure that even if an attacker gains access to a system, they cannot easily exploit this vulnerability without proper capabilities. This vulnerability serves as a reminder of the critical importance of kernel security validation and the potential for information disclosure vulnerabilities to undermine overall system security posture.