CVE-2013-1959 in Linux
Summary
by MITRE
kernel/user_namespace.c in the Linux kernel before 3.8.9 does not have appropriate capability requirements for the uid_map and gid_map files, which allows local users to gain privileges by opening a file within an unprivileged process and then modifying the file within a privileged process.
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Analysis
by VulDB Data Team • 06/15/2024
The vulnerability described in CVE-2013-1959 represents a critical privilege escalation flaw within the Linux kernel's user namespace implementation. This issue affects kernel versions prior to 3.8.9 and stems from insufficient capability checks in the uid_map and gid_map files. The core problem lies in the improper handling of file access controls within user namespaces, where the kernel fails to enforce adequate security boundaries between privileged and unprivileged execution contexts. This weakness creates a fundamental breach in the kernel's security model, allowing attackers to exploit the trust relationship between processes running under different privilege levels.
The technical flaw manifests through a specific race condition and capability bypass mechanism. In user namespaces, uid_map and gid_map files are used to map user and group IDs between the host namespace and the user namespace. The vulnerability occurs because these files lack proper capability requirements for modification operations, enabling local users to manipulate these mapping files even when running in unprivileged contexts. When an attacker opens a file within an unprivileged process and subsequently modifies the corresponding uid_map or gid_map file within a privileged process, they can effectively escalate their privileges. This occurs because the kernel does not properly validate whether the modifying process has the necessary capabilities to alter these critical mapping files. The flaw operates at the intersection of process privilege management and namespace isolation, violating fundamental security principles that should prevent unprivileged code from manipulating privileged system resources.
The operational impact of this vulnerability is severe and far-reaching within Linux environments. Local attackers can leverage this flaw to escalate their privileges from unprivileged user accounts to root access, effectively bypassing the entire privilege separation model that the kernel employs. This capability allows for complete system compromise, enabling attackers to execute arbitrary code with root privileges, modify system files, establish persistent backdoors, and gain access to all system resources. The vulnerability is particularly dangerous because it requires minimal privileges to exploit and can be automated through simple scripts that manipulate the mapping files. Attackers can use this vulnerability in various attack scenarios including container escape, sandbox bypass, and general privilege escalation attacks against systems running vulnerable kernel versions. The impact extends beyond individual systems to potentially compromise entire network infrastructures where such systems are deployed.
Mitigation strategies for CVE-2013-1959 focus primarily on kernel version updates and system hardening measures. The most effective solution involves upgrading to Linux kernel version 3.8.9 or later, where the vulnerability has been patched through proper capability enforcement in the user namespace implementation. System administrators should also implement additional security measures such as restricting access to user namespace capabilities through sysctl parameters and monitoring for unauthorized modifications to uid_map and gid_map files. The patch addresses the underlying CWE-284 weakness related to improper access control by ensuring that appropriate capability checks are enforced before allowing modifications to critical mapping files. Organizations should also consider implementing process monitoring and file integrity checking mechanisms to detect potential exploitation attempts. This vulnerability aligns with ATT&CK technique T1068 which covers privilege escalation through local exploitation, and demonstrates the importance of proper privilege separation in kernel security models. The fix reinforces the principle that critical system resources should never be accessible to unprivileged processes without appropriate capability validation, thereby preventing the type of privilege escalation that this vulnerability enabled.