Source: cve@mitre.org
The linux-2.4.21-mlock.patch in Red Hat Enterprise Linux 3 does not properly maintain the mlock page count when one process unlocks pages that belong to another process, which allows local users to mlock more memory than specified by the rlimit.
Local privilege escalation is possible due to a flaw in the memory locking mechanism of Red Hat Enterprise Linux 3. This vulnerability allows a local user to bypass memory limits, potentially leading to denial-of-service or the ability to execute arbitrary code with elevated privileges by exhausting system resources.
Step 1: Initial Setup: A local user logs into the vulnerable system.
Step 2: Resource Limit Check: The user's current resource limits (e.g., RLIMIT_MEMLOCK) are checked and noted.
Step 3: Memory Locking: The user attempts to lock a certain amount of memory using mlock(), within the bounds of their current resource limits.
Step 4: Cross-Process Unlock (Exploitation): A second process, or a thread within the same process, unlocks memory that was locked by the first process. Due to the vulnerability, the kernel incorrectly updates the mlock page count.
Step 5: Repeated Locking: The first process repeatedly calls mlock() and munlock() in a carefully crafted sequence, exploiting the incorrect page count to bypass the RLIMIT_MEMLOCK limit.
Step 6: Memory Exhaustion: The user continues to lock memory, eventually exhausting the available system memory, leading to a denial-of-service condition or other memory-related issues.
The vulnerability stems from an improper handling of the mlock page count within the linux-2.4.21-mlock.patch applied to Red Hat Enterprise Linux 3. Specifically, the kernel fails to accurately track the number of locked pages when one process unlocks pages that were locked by another process. This leads to an integer underflow or incorrect accounting of locked memory. The flaw allows a malicious user to repeatedly call mlock() and munlock() in a specific sequence, manipulating the kernel's internal page count. By exploiting this, the user can effectively bypass the resource limits imposed by rlimit, leading to the allocation of excessive memory. This can be used to exhaust available system memory, leading to a denial-of-service (DoS) condition, or in more complex scenarios, potentially be leveraged to overwrite other critical kernel data structures, enabling arbitrary code execution. The root cause is a logic error in the kernel's memory management code, specifically in the interaction between mlock() and munlock() calls across different processes.
Due to the age of the vulnerability, it's unlikely to be directly associated with specific APT groups. However, any threat actor with access to a vulnerable system could exploit it. The impact of the vulnerability is local privilege escalation, which can be a precursor to more sophisticated attacks. CISA KEV status: Not Listed
Monitor system logs for unusual activity related to memory allocation and deallocation (e.g., excessive use of mlock() and munlock() system calls).
Analyze system memory usage patterns for anomalies, such as unexpectedly high memory consumption by a single process.
Use system monitoring tools (e.g., top, vmstat, free) to track memory usage and identify processes that are consuming excessive memory.
Examine audit logs for suspicious system calls related to memory management, such as mlock() and munlock(), especially when used by low-privilege users.
Implement host-based intrusion detection systems (HIDS) to detect anomalous behavior related to memory allocation and process behavior.
Apply the security patch provided by Red Hat for the affected version of Red Hat Enterprise Linux 3. This patch addresses the incorrect handling of the mlock page count.
Upgrade to a supported and patched version of Red Hat Enterprise Linux. This is the most effective long-term solution.
Implement least privilege principles, limiting the permissions of users and processes to the minimum necessary for their tasks.
Regularly audit system configurations and security settings to ensure they are properly configured and up-to-date.
Monitor system logs and implement intrusion detection systems to detect and respond to suspicious activity.