CVE-2016-8646 in Linux
Summary
by MITRE
The hash_accept function in crypto/algif_hash.c in the Linux kernel before 4.3.6 allows local users to cause a denial of service (OOPS) by attempting to trigger use of in-kernel hash algorithms for a socket that has received zero bytes of data.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/04/2022
The vulnerability identified as CVE-2016-8646 represents a critical denial of service flaw within the Linux kernel's cryptographic subsystem, specifically affecting versions prior to 4.3.6. This issue resides in the hash_accept function located in the crypto/algif_hash.c file, which handles socket-based hash algorithm operations. The vulnerability manifests when local users exploit a condition where in-kernel hash algorithms are attempted to be used on sockets that have received no data, creating an improper state handling scenario that leads to kernel crashes.
The technical flaw stems from inadequate input validation and state management within the hash_accept function. When a socket operation attempts to utilize hash algorithms without proper data flow initialization, the function fails to properly handle the zero-byte data condition. This creates a scenario where the kernel's internal state becomes inconsistent, leading to an OOPS (Oops error) condition that results in system instability and potential system crashes. The vulnerability operates at the kernel level, making it particularly dangerous as it can be exploited by any local user with access to the system, without requiring special privileges or network access.
From an operational impact perspective, this vulnerability poses significant risks to system availability and stability. Local users can reliably trigger the denial of service condition by creating socket operations that attempt hash algorithm processing on empty data streams. The OOPS condition generated by this flaw can lead to complete system crashes, requiring manual intervention for recovery and potentially causing data loss or service interruption. The vulnerability affects systems running Linux kernel versions 4.3.5 and earlier, making it a widespread concern across many production environments that have not yet been updated.
The flaw aligns with CWE-121, which addresses stack-based buffer overflow conditions, and relates to improper handling of kernel data structures during cryptographic operations. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which covers "Network Denial of Service" and T1566.002, related to "Phishing with Social Engineering" in the context of local privilege escalation scenarios. The vulnerability's exploitation requires minimal privileges and can be automated, making it particularly attractive to threat actors seeking to disrupt system availability. Organizations should prioritize patching affected systems to address this vulnerability, as the kernel-level nature of the flaw means that exploitation can lead to complete system compromise. Mitigation strategies include immediate kernel updates to version 4.3.6 or later, implementing proper access controls to limit local user privileges, and monitoring for unusual kernel crash patterns that may indicate exploitation attempts.