CVE-2008-3528 in Linux
Summary
by MITRE
The error-reporting functionality in (1) fs/ext2/dir.c, (2) fs/ext3/dir.c, and possibly (3) fs/ext4/dir.c in the Linux kernel 2.6.26.5 does not limit the number of printk console messages that report directory corruption, which allows physically proximate attackers to cause a denial of service (temporary system hang) by mounting a filesystem that has corrupted dir->i_size and dir->i_blocks values and performing (a) read or (b) write operations. NOTE: there are limited scenarios in which this crosses privilege boundaries.
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Analysis
by VulDB Data Team • 08/20/2019
The vulnerability described in CVE-2008-3528 represents a critical denial of service weakness within the Linux kernel's filesystem error reporting mechanisms. This issue affects the ext2, ext3, and potentially ext4 filesystem implementations, specifically within the directory handling code located in the filesystem layer. The flaw manifests when the kernel's error reporting functionality fails to impose limits on the number of printk console messages generated during directory corruption detection. This behavior creates a scenario where maliciously crafted filesystems can trigger excessive logging activity that overwhelms system resources.
The technical root cause of this vulnerability lies in the absence of message rate limiting within the kernel's directory corruption reporting code. When filesystems with corrupted dir->i_size and dir->i_blocks values are mounted, the kernel's error reporting mechanism continuously generates printk messages without proper throttling. This unbounded message generation occurs during both read and write operations, creating a condition where the console output buffer fills rapidly and system resources become consumed. The vulnerability specifically targets the directory structure integrity checking mechanisms that are part of the standard filesystem operations.
Attackers exploiting this vulnerability need only be physically proximate to the target system, as the attack vector involves mounting a specially crafted filesystem image. The attack can be executed through simple read or write operations on the corrupted filesystem, making it particularly dangerous in environments where untrusted filesystems might be mounted automatically. The temporary system hang that results from this vulnerability can persist until manual intervention occurs, potentially causing significant service disruption. This vulnerability demonstrates how filesystem-level errors can be leveraged to create system-wide availability issues without requiring elevated privileges, though the attack scope is limited by the physical proximity requirement.
The operational impact of this vulnerability extends beyond simple system hangs, as the excessive printk messages can consume substantial amounts of memory and CPU cycles during the logging process. This behavior can be particularly problematic in embedded systems or environments where console output is redirected to limited resources. The vulnerability affects all versions of the Linux kernel through 2.6.26.5, making it a widespread concern across many deployed systems. The limited privilege boundary crossing mentioned in the description indicates that while the vulnerability itself does not allow privilege escalation, it can be exploited by attackers who have physical access to the system or can mount untrusted filesystems.
From a cybersecurity perspective, this vulnerability aligns with CWE-770, which addresses the allocation of resources without proper limits or throttling mechanisms. The issue also relates to ATT&CK technique T1499.001, which involves the exploitation of resource consumption vulnerabilities to cause denial of service conditions. The vulnerability represents a classic example of how kernel-level resource management flaws can be exploited to create system instability, and it underscores the importance of implementing proper bounds checking and rate limiting in kernel subsystems. Mitigation strategies typically involve applying kernel patches that introduce proper message rate limiting and implementing filesystem access controls to prevent mounting of untrusted filesystems. The vulnerability also highlights the need for comprehensive testing of error handling paths in kernel code, particularly in filesystem implementations where corrupted data can trigger excessive logging behavior.