CVE-2016-4470 in Android
Summary
by MITRE
The key_reject_and_link function in security/keys/key.c in the Linux kernel through 4.6.3 does not ensure that a certain data structure is initialized, which allows local users to cause a denial of service (system crash) via vectors involving a crafted keyctl request2 command.
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Analysis
by VulDB Data Team • 09/15/2022
The vulnerability described in CVE-2016-4470 resides within the Linux kernel's key management subsystem, specifically in the key_reject_and_link function located in security/keys/key.c. This flaw represents a classic case of uninitialized memory access that can be exploited by local attackers to trigger system crashes. The vulnerability affects Linux kernel versions through 4.6.3 and demonstrates how improper initialization of data structures can lead to critical system instability. The issue occurs when processing crafted keyctl requests that involve the key_reject_and_link function, which fails to properly initialize a critical data structure before use. This oversight creates a scenario where the kernel's key management system can be manipulated to execute code paths that result in memory corruption and ultimately system crashes. The vulnerability is particularly concerning because it operates at the kernel level, providing attackers with a pathway to achieve denial of service conditions that can bring entire systems to their knees. Attackers need only possess local access to exploit this vulnerability, making it a significant concern for systems where local privilege escalation or unauthorized access is possible.
The technical implementation of this vulnerability stems from a failure in the kernel's key management infrastructure to properly initialize memory structures before utilizing them in cryptographic operations. When the key_reject_and_link function processes certain keyctl commands, it assumes that a particular data structure has been properly initialized, but this assumption proves incorrect under specific attack conditions. This uninitialized data structure access falls under the common software security weakness category of CWE-457, which deals with use of uninitialized variables, and more specifically relates to CWE-476, which addresses null pointer dereference conditions. The function's inability to validate the initialization state of its data structures creates a predictable execution path that can be exploited by attackers to manipulate kernel memory layouts. The vulnerability manifests as a system crash because the uninitialized memory contains arbitrary values that, when interpreted as pointers or control structures, cause the kernel to access invalid memory addresses or execute malformed instructions. This type of memory corruption directly violates kernel security principles and can potentially be leveraged for more sophisticated attacks if combined with other vulnerabilities.
From an operational perspective, this vulnerability presents a significant risk to Linux systems that rely on kernel key management services for credential handling, authentication, and access control. The denial of service impact affects system availability and can be particularly damaging in mission-critical environments where uptime is essential. While the vulnerability requires local access to exploit, this limitation does not mitigate its potential impact, as local attackers can often escalate privileges or gain access through various attack vectors. The vulnerability affects systems running kernel versions through 4.6.3, which includes numerous enterprise and server deployments where kernel stability is paramount. Organizations using affected kernel versions face the risk of unauthorized system downtime, which can result in service interruptions, data loss, and operational disruptions. The exploitability of this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, though in this case the attack vector is local rather than network-based. The vulnerability's impact extends beyond simple system crashes, as it can potentially be used to disrupt critical services, cause data corruption, or create conditions that allow for further exploitation.
Mitigation strategies for CVE-2016-4470 involve immediate kernel updates to versions that contain the necessary patches addressing the uninitialized memory access issue. System administrators should prioritize applying security patches from their respective kernel vendors, as the vulnerability has been resolved through proper initialization of the affected data structures. Organizations should also implement monitoring systems to detect unusual keyctl activity that might indicate exploitation attempts, particularly focusing on local processes that make frequent keyctl requests. The patch for this vulnerability typically involves adding proper initialization checks before the key_reject_and_link function processes keyctl commands, ensuring that all required data structures are properly allocated and initialized. Additionally, system hardening measures such as restricting local access to privileged accounts, implementing proper access controls for keyctl commands, and monitoring for suspicious system behavior can help reduce the attack surface. Security teams should also consider implementing kernel module whitelisting or lockdown mechanisms to prevent unauthorized modification of kernel components. Regular vulnerability assessments and kernel security audits should be conducted to identify similar issues in other kernel subsystems, as this vulnerability demonstrates how seemingly minor initialization errors can create significant security risks. The remediation process should include thorough testing of patched kernels in controlled environments to ensure that the fix does not introduce compatibility issues with existing system configurations or applications that depend on kernel key management functionality.