CVE-2017-9211 in Linux
Summary
by MITRE
The crypto_skcipher_init_tfm function in crypto/skcipher.c in the Linux kernel through 4.11.2 relies on a setkey function that lacks a key-size check, which allows local users to cause a denial of service (NULL pointer dereference) via a crafted application.
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability identified as CVE-2017-9211 represents a critical flaw in the Linux kernel's cryptographic subsystem that affects versions through 4.11.2. This issue resides within the crypto/skcipher.c file and specifically targets the crypto_skcipher_init_tfm function which handles the initialization of symmetric key cipher transformations. The vulnerability stems from an insufficient validation mechanism that fails to properly verify key sizes during the cryptographic algorithm setup process, creating a pathway for malicious exploitation that can result in system instability and service disruption.
The technical root cause of this vulnerability lies in the absence of proper key size validation within the setkey function that operates as part of the crypto_skcipher_init_tfm routine. When a cryptographic algorithm is initialized, the system should validate that the provided key meets the minimum size requirements for the specific cipher being configured. However, in this case, the validation process is incomplete or missing entirely, allowing malformed or improperly sized keys to be processed without proper bounds checking. This flaw creates a condition where a NULL pointer dereference can occur during subsequent cryptographic operations, as the system attempts to access memory locations that have not been properly allocated or initialized.
The operational impact of CVE-2017-9211 is significant as it enables local users to trigger a denial of service condition that can effectively crash the kernel or render system services unavailable. The vulnerability is particularly dangerous because it operates at the kernel level where a successful exploitation can lead to complete system instability, requiring manual intervention for recovery. Since the attack vector involves a local user executing a crafted application, the threat surface is limited to users with existing system access, but this still represents a serious security concern given that privilege escalation or lateral movement could potentially be achieved through additional attack vectors. The NULL pointer dereference condition typically results in kernel panics or system crashes that require system rebooting to restore normal operations.
This vulnerability maps to CWE-125 Out-of-bounds Read and CWE-476 NULL Pointer Dereference within the Common Weakness Enumeration framework, highlighting the fundamental nature of the flaw as both an improper input validation issue and a memory management error. From the MITRE ATT&CK framework perspective, this vulnerability could be categorized under T1068 Valid Accounts and T1499 Endpoint Denial of Service as it leverages existing local user privileges to cause system-wide disruption. The vulnerability demonstrates how cryptographic implementations must maintain rigorous input validation standards to prevent exploitation of kernel-level components. The flaw also represents a failure in the principle of least privilege as the kernel fails to properly validate cryptographic parameters before processing them, potentially allowing attackers to craft malicious inputs that bypass normal security checks.
Mitigation strategies for CVE-2017-9211 should focus on immediate kernel updates to versions 4.11.3 or later where the vulnerability has been patched. Organizations should implement comprehensive monitoring for unauthorized local access attempts and establish robust patch management procedures to ensure timely deployment of security updates. The fix implemented by the Linux kernel team involved adding proper key size validation checks within the setkey function to prevent invalid key sizes from being processed, thereby eliminating the NULL pointer dereference condition. Additionally, system administrators should consider implementing additional security measures such as restricting local user privileges where possible and monitoring for unusual kernel-level activity that could indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify similar issues in other cryptographic implementations within the system infrastructure.