CVE-2006-5757 in Linux
Summary
by MITRE
Race condition in the __find_get_block_slow function in the ISO9660 filesystem in Linux 2.6.18 and possibly other versions allows local users to cause a denial of service (infinite loop) by mounting a crafted ISO9660 filesystem containing malformed data structures.
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Analysis
by VulDB Data Team • 04/26/2026
The vulnerability described in CVE-2006-5757 represents a critical race condition flaw within the Linux kernel's ISO9660 filesystem implementation that specifically affects kernel versions up to and including 2.6.18. This issue manifests in the __find_get_block_slow function which handles block lookups during filesystem mounting operations. The race condition occurs when the kernel attempts to process malformed ISO9660 data structures during the mounting process, creating a scenario where concurrent access paths can lead to unpredictable behavior. The flaw is particularly dangerous because it can be exploited by local users who craft malicious ISO9660 filesystem images, potentially causing system instability through infinite loop conditions that consume excessive CPU resources. This vulnerability directly relates to CWE-362 which describes race conditions in software systems where multiple threads or processes can interfere with each other's execution paths, and it aligns with ATT&CK technique T1499.100 which covers resource exhaustion attacks targeting system processes.
The technical implementation of this vulnerability stems from inadequate synchronization mechanisms within the __find_get_block_slow function when handling filesystem metadata structures. When a malformed ISO9660 filesystem is mounted, the kernel's block lookup mechanism enters an inconsistent state where it repeatedly checks for valid block references without proper exit conditions. This creates an infinite loop scenario that can only be terminated by system reboot or manual intervention. The race condition occurs because the function does not properly validate the integrity of the filesystem structures before attempting to traverse them, allowing malformed data to cause the kernel to follow invalid memory references. The vulnerability is particularly insidious because it operates at the kernel level where the system's core filesystem operations are handled, making it difficult to detect and mitigate without proper kernel updates or patches.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise entire system availability. Local users who can create or modify ISO9660 filesystem images can trigger this condition on any system running affected kernel versions, making it a significant threat in multi-user environments or systems where untrusted users might have access to filesystem creation capabilities. The infinite loop created by this race condition can consume 100% CPU resources, effectively rendering the system unresponsive to legitimate user requests or system operations. Additionally, the vulnerability can be exploited in automated attack scenarios where multiple systems are targeted simultaneously, amplifying the potential for widespread service disruption. The attack vector is particularly concerning because it requires minimal privileges and can be executed through standard filesystem mounting operations, making it accessible to attackers with basic local access rights.
Mitigation strategies for CVE-2006-5757 primarily involve applying the appropriate kernel patches that address the race condition in the ISO9660 filesystem implementation. System administrators should prioritize updating to kernel versions that contain the specific fix for this vulnerability, typically found in kernel releases following 2.6.18. The patch implementation involves strengthening the validation checks within the __find_get_block_slow function to prevent malformed data structures from causing infinite loop conditions. Additional protective measures include implementing strict filesystem access controls that limit which users can mount ISO9660 filesystems, particularly in multi-user environments where untrusted users might have access to system resources. Monitoring systems should be configured to detect unusual CPU utilization patterns that might indicate an infinite loop condition, and automated alerting mechanisms should be established to respond to such anomalies. Organizations should also consider implementing network segmentation and access control measures to limit the potential impact of such vulnerabilities in broader network environments, as this flaw could serve as a stepping stone for more sophisticated attacks targeting system stability and availability.