CVE-2010-2537 in Linux
Summary
by MITRE
The btrfs_ioctl_clone function in fs/btrfs/ioctl.c in the Linux kernel before 2.6.35 allows local users to overwrite an append-only file via a (1) BTRFS_IOC_CLONE or (2) BTRFS_IOC_CLONE_RANGE ioctl call that specifies this file as a donor.
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Analysis
by VulDB Data Team • 09/25/2021
The vulnerability described in CVE-2010-2537 represents a critical access control flaw in the Linux kernel's BTRFS filesystem implementation that enables local privilege escalation through improper file permission handling. This issue specifically affects the btrfs_ioctl_clone function located in fs/btrfs/ioctl.c, which governs the cloning operations within the BTRFS filesystem. The vulnerability arises from the kernel's failure to properly validate file permissions when processing clone operations, creating a scenario where malicious local users can exploit this weakness to overwrite files marked as append-only, which should normally be protected from such modifications.
The technical flaw manifests through two distinct ioctl calls that can be exploited by attackers: BTRFS_IOC_CLONE and BTRFS_IOC_CLONE_RANGE. These operations allow for efficient data copying within the BTRFS filesystem, but the kernel implementation lacks proper validation of the target file's append-only attribute. When a user specifies an append-only file as the donor in a clone operation, the system should prevent such modifications to maintain file integrity and security policies. However, the vulnerability allows the clone operation to proceed without checking whether the target file has restrictive permissions that should prevent overwriting, effectively bypassing the append-only protection mechanism that is fundamental to Unix-like file systems.
The operational impact of this vulnerability extends beyond simple file corruption, as it undermines the fundamental security model of the Linux filesystem by allowing unauthorized modifications to protected files. An attacker with local access can leverage this flaw to overwrite system-critical files, potentially leading to privilege escalation or denial of service conditions. This vulnerability is particularly dangerous because it operates at the kernel level, where the attacker's actions are not subject to typical user-space permission checks. The flaw affects all Linux systems running kernel versions prior to 2.6.35, making it a widespread concern for organizations maintaining older kernel versions. The vulnerability aligns with CWE-284, which addresses improper access control, and represents a classic case of privilege escalation through improper validation of file permissions.
Security implications of this vulnerability are significant as it allows local users to circumvent the append-only attribute that is commonly used to protect critical system files and logs. The exploit requires only local access to the system, making it particularly concerning for multi-user environments where users may not have elevated privileges. Attackers can use this vulnerability to modify system configuration files, log files, or other sensitive data that should remain immutable. The vulnerability also relates to ATT&CK technique T1068, which involves exploiting local privileges to escalate access, and T1566, which covers social engineering tactics that could be used to gain local access. Organizations should immediately patch their systems to kernel version 2.6.35 or later, as this vulnerability has been widely exploited in the wild and represents a serious threat to system integrity and security.
This vulnerability demonstrates the importance of proper input validation and access control enforcement even within kernel-level filesystem operations. The flaw highlights the need for comprehensive security testing of filesystem implementations and proper adherence to security principles such as least privilege and defense in depth. System administrators should implement additional monitoring to detect unauthorized file modifications and ensure that all systems are running patched kernel versions. The vulnerability also underscores the importance of maintaining up-to-date security patches and following secure coding practices that prevent similar issues in other filesystem implementations. Organizations should conduct regular security assessments of their kernel configurations and file system permissions to identify and remediate similar vulnerabilities that may exist in their environments.