CVE-2009-2406 in Linux
Summary
by MITRE
Stack-based buffer overflow in the parse_tag_11_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 not ensuring that the key signature length in a Tag 11 packet is compatible with the key signature buffer size.
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Analysis
by VulDB Data Team • 08/13/2021
The vulnerability described in CVE-2009-2406 represents a critical stack-based buffer overflow within the eCryptfs subsystem of the Linux kernel, specifically affecting versions prior to 2.6.30.4. This flaw exists in the parse_tag_11_packet function located in fs/ecryptfs/keystore.c, which processes cryptographic key data during eCryptfs file operations. The vulnerability stems from inadequate validation of key signature lengths within Tag 11 packets, creating a scenario where maliciously crafted eCryptfs files can trigger memory corruption. The eCryptfs filesystem is designed for transparent encryption of files and directories, making it a critical component for data protection in Linux environments. When a local user presents a specially crafted eCryptfs file, the kernel's parsing mechanism fails to verify that the key signature length matches the allocated buffer size, leading to potential stack corruption. This type of vulnerability falls under CWE-121, stack-based buffer overflow, which is classified as a fundamental memory safety issue that can lead to system instability or privilege escalation. The ATT&CK framework categorizes this as a privilege escalation technique through kernel exploitation, as local users can leverage such flaws to gain elevated system privileges.
The technical execution of this vulnerability involves the manipulation of eCryptfs file structures where Tag 11 packets contain key signature data that must be processed by the kernel's cryptographic subsystem. During normal operation, the kernel allocates a fixed-size buffer for storing key signatures, but the parse_tag_11_packet function does not properly validate the incoming data length against the buffer capacity. When a crafted file contains a key signature that exceeds the allocated buffer space, the excess data overflows into adjacent stack memory locations, potentially corrupting critical kernel data structures or executing arbitrary code. The impact extends beyond simple denial of service, as the buffer overflow can be leveraged for privilege escalation attacks when the overflow affects control flow data such as return addresses or function pointers. The vulnerability specifically targets the kernel's memory management and cryptographic processing capabilities, making it particularly dangerous in environments where eCryptfs is actively used for file encryption. This flaw demonstrates the importance of input validation in kernel space operations, as the lack of proper bounds checking in cryptographic parsing functions can create exploitable conditions.
The operational impact of CVE-2009-2406 presents significant risks to Linux systems utilizing eCryptfs for data encryption, as local users can exploit this vulnerability to either crash the system or potentially gain root privileges. Denial of service attacks can be executed simply by creating malicious eCryptfs files that trigger the buffer overflow condition, causing system crashes and rendering the encryption subsystem unusable. However, the more serious concern lies in the potential for privilege escalation, where an attacker could manipulate the stack overflow to overwrite kernel memory with malicious code or alter execution control flow. Systems running affected kernel versions are particularly vulnerable because the vulnerability exists in core cryptographic processing functions that handle file access operations. The exploitability of this vulnerability is enhanced by the fact that it requires minimal privileges, as local users can craft malicious files without requiring special permissions. Organizations using eCryptfs for enterprise file encryption or personal data protection face substantial risk from this vulnerability, as it undermines the security guarantees provided by the encryption subsystem. The vulnerability's impact is further amplified by the fact that it affects the kernel's core cryptographic processing, making it difficult to isolate and patch without full system updates.
Mitigation strategies for CVE-2009-2406 primarily focus on immediate kernel version upgrades to 2.6.30.4 or later, which contain the necessary patches to address the buffer overflow condition. System administrators should prioritize patching affected systems and verify that all eCryptfs operations are properly secured through updated kernel versions. Additional defensive measures include implementing strict file access controls and monitoring for unusual eCryptfs file creation activities that might indicate exploitation attempts. Organizations should also consider disabling eCryptfs functionality on systems where it is not essential, reducing the attack surface for this particular vulnerability. The patch for this vulnerability addresses the core issue by implementing proper bounds checking on key signature lengths before copying data into the fixed-size buffer. Security monitoring should focus on detecting attempts to create or access malformed eCryptfs files, as these activities may precede exploitation attempts. Regular kernel updates and security audits are essential for maintaining protection against similar vulnerabilities in cryptographic subsystems, as this flaw highlights the need for rigorous input validation in kernel space operations. The vulnerability also emphasizes the importance of adhering to security best practices in kernel development, particularly regarding memory management and buffer handling in cryptographic processing functions.