CVE-2009-2407 in Linux
Summary
by MITRE
Heap-based buffer overflow in the parse_tag_3_packet function in fs/ecryptfs/keystore.c in the eCryptfs subsystem in the Linux kernel before 2.6.30.4 allows local users to cause a denial of service (system crash) or possibly gain privileges via vectors involving a crafted eCryptfs file, related to a large encrypted key size in a Tag 3 packet.
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Analysis
by VulDB Data Team • 08/13/2021
The vulnerability described in CVE-2009-2407 represents a critical heap-based buffer overflow within the eCryptfs subsystem of the Linux kernel, specifically within the parse_tag_3_packet function located in fs/ecryptfs/keystore.c. This flaw exists in kernel versions prior to 2.6.30.4 and demonstrates a classic memory corruption issue that can be exploited by local attackers to either crash the system or potentially escalate privileges. The vulnerability manifests when processing crafted eCryptfs files containing malformed Tag 3 packets with excessively large encrypted key sizes, creating a scenario where the kernel fails to properly validate input data before attempting to allocate memory for processing.
The technical implementation of this vulnerability stems from inadequate bounds checking within the eCryptfs parsing logic, where the parse_tag_3_packet function does not sufficiently validate the size parameter of encrypted keys contained within Tag 3 packets. When a maliciously crafted eCryptfs file is processed, the function attempts to allocate heap memory based on an untrusted size value that can exceed the allocated buffer boundaries. This heap corruption occurs because the kernel's memory management routines do not perform proper validation of the encrypted key size before proceeding with memory allocation, leading to a situation where adjacent memory regions become overwritten or corrupted. The vulnerability is classified as a heap-based buffer overflow under CWE-122, which specifically addresses insufficient checking of heap buffer bounds, and represents a direct violation of memory safety principles in kernel space operations.
The operational impact of this vulnerability extends beyond simple system crashes to potentially enable privilege escalation, making it particularly dangerous for local attackers who can leverage the heap corruption to gain elevated system privileges. When the buffer overflow occurs during processing of the malformed Tag 3 packet, the kernel's memory corruption can lead to unpredictable behavior including system crashes, data corruption, or in some scenarios, arbitrary code execution with kernel privileges. The denial of service aspect affects system stability and availability, while the privilege escalation potential compromises the entire security model of the Linux kernel. This vulnerability directly relates to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', and demonstrates how kernel-level memory corruption can be weaponized for system compromise. The local nature of the attack means that any user with access to the system can potentially exploit this vulnerability, making it particularly concerning for multi-user environments.
Mitigation strategies for CVE-2009-2407 primarily involve upgrading to kernel versions 2.6.30.4 or later, where the vulnerability has been patched through enhanced input validation and proper bounds checking in the eCryptfs subsystem. System administrators should prioritize patch management and ensure all Linux systems are running patched kernel versions to prevent exploitation. Additional defensive measures include implementing strict file access controls and monitoring for unusual eCryptfs file operations, though these are secondary measures since the vulnerability exists within kernel space processing. The patch implemented in the fixed kernel versions addresses the root cause by adding proper validation of encrypted key sizes before memory allocation occurs, preventing the heap overflow condition from being triggered. Organizations should also consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and kernel module signing to further reduce the attack surface and mitigate potential exploitation of similar vulnerabilities in the future.