CVE-2007-0006 in Linux
Summary
by MITRE
The key serial number collision avoidance code in the key_alloc_serial function in Linux kernel 2.6.9 up to 2.6.20 allows local users to cause a denial of service (crash) via vectors that trigger a null dereference, as originally reported as "spinlock CPU recursion."
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Analysis
by VulDB Data Team • 07/14/2019
The vulnerability described in CVE-2007-0006 represents a critical flaw in the Linux kernel's key management subsystem that manifests through improper handling of serial number generation during key allocation. This issue affects kernel versions from 2.6.9 through 2.6.20, creating a condition where local attackers can exploit a null dereference scenario to crash the system. The vulnerability stems from the key_alloc_serial function which is responsible for generating unique serial numbers for kernel keys, a fundamental component of the kernel's security infrastructure. When specific conditions are met during key allocation operations, the function fails to properly initialize or validate serial number generation, leading to a state where subsequent operations attempt to dereference null pointers.
The technical implementation of this vulnerability involves the kernel's key management subsystem where the key_alloc_serial function is designed to prevent serial number collisions by maintaining proper sequencing. However, the flaw occurs when the function encounters certain race conditions or specific input patterns that cause it to return a null value where a valid serial number should be generated. This null return value propagates through the kernel's key management code path, eventually leading to a null pointer dereference when the system attempts to access memory locations associated with the invalid serial number. The original reporting term "spinlock CPU recursion" indicates that the system's spinlock mechanisms become entangled during the crash condition, causing the CPU to enter a recursive locking state that ultimately results in system instability and potential complete system crash.
The operational impact of this vulnerability extends beyond simple denial of service as it represents a fundamental breakdown in kernel stability that can be exploited by local users with minimal privileges. The vulnerability allows attackers to cause system-wide crashes that can result in complete system downtime, potentially leading to data loss or service disruption in environments where kernel stability is critical. This particular flaw affects the core key management infrastructure that underpins various security mechanisms including cryptographic key handling, access control systems, and other kernel-level security features that depend on the proper functioning of the key subsystem. The vulnerability's exploitation requires local access to the system but can result in severe operational consequences including complete system compromise through sustained denial of service attacks.
Mitigation strategies for CVE-2007-0006 involve immediate kernel updates to versions that contain the patched key_alloc_serial function implementation. The fix addresses the root cause by ensuring proper initialization of serial number generation and adding appropriate null checks before pointer dereference operations. System administrators should prioritize patching affected systems and monitor for any signs of exploitation attempts, particularly in environments where local user access is not strictly controlled. The vulnerability aligns with CWE-476 which describes null pointer dereference conditions, and represents a classic example of how improper error handling in kernel code can lead to system instability. From an ATT&CK perspective, this vulnerability could be leveraged as part of a broader attack chain where local privilege escalation or persistent denial of service capabilities are employed to maintain access or disrupt system availability, though the vulnerability itself does not directly enable privilege escalation beyond the initial denial of service condition.