CVE-2009-3624 in Linux
Summary
by MITRE
The get_instantiation_keyring function in security/keys/keyctl.c in the KEYS subsystem in the Linux kernel before 2.6.32-rc5 does not properly maintain the reference count of a keyring, which allows local users to gain privileges or cause a denial of service (OOPS) via vectors involving calls to this function without specifying a keyring by ID, as demonstrated by a series of keyctl request2 and keyctl list commands.
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Analysis
by VulDB Data Team • 08/25/2021
The vulnerability described in CVE-2009-3624 resides within the Linux kernel's KEYS subsystem, specifically in the get_instantiation_keyring function located in security/keys/keyctl.c. This flaw represents a critical reference counting error that affects kernel versions prior to 2.6.32-rc5, creating a pathway for local attackers to exploit system privileges through improper keyring management. The vulnerability manifests when the function fails to correctly maintain reference counts for keyrings, leading to potential privilege escalation or system instability.
The technical exploitation of this vulnerability occurs through deliberate manipulation of keyctl commands without specifying a keyring by ID, particularly leveraging keyctl request2 and keyctl list operations. This improper reference count handling creates a scenario where keyring objects can be prematurely freed or accessed after deallocation, resulting in kernel memory corruption. The flaw stems from inadequate validation and management of keyring reference counts during instantiation operations, which directly violates proper kernel memory management principles and can lead to unpredictable system behavior.
From an operational perspective, this vulnerability poses significant risks to system integrity and availability. Local users can leverage this flaw to either escalate their privileges to root level access or trigger kernel oops conditions that result in system crashes and denial of service. The impact extends beyond simple privilege escalation as the reference counting error can cause cascading failures within the kernel's key management infrastructure, potentially affecting other security mechanisms that depend on proper keyring handling. This vulnerability directly aligns with CWE-476 which addresses null pointer dereferences and improper reference counting issues in kernel code.
The exploitation pattern demonstrates sophisticated understanding of kernel internals and memory management principles, as attackers must carefully orchestrate multiple keyctl operations to trigger the reference count inconsistency. This type of vulnerability typically requires deep knowledge of kernel security subsystems and can be classified under ATT&CK technique T1068 which covers 'Exploitation for Privilege Escalation'. The attack vector specifically targets local users with existing system access, making it particularly dangerous in multi-user environments where privilege separation is critical for system security.
Mitigation strategies for CVE-2009-3624 require immediate kernel version updates to 2.6.32-rc5 or later, where the reference counting issue has been properly addressed through enhanced validation and management of keyring objects. System administrators should also implement monitoring for unusual keyctl activity patterns and consider restricting keyctl command usage to authorized users only. The fix involves proper reference count management within the get_instantiation_keyring function to ensure that keyring objects remain valid throughout their intended usage period. Additionally, organizations should conduct comprehensive security assessments of their kernel configurations and implement proper access controls to minimize the attack surface for such local privilege escalation vulnerabilities.