CVE-2024-26602: Linux Kernel DOS Vulnerability

CVE-2024-26602 Overview

CVE-2024-26602 is a Denial of Service vulnerability in the Linux kernel's sys_membarrier system call implementation. The vulnerability exists in the scheduler's memory barrier functionality, where the lack of proper serialization allows a local attacker to repeatedly invoke sys_membarrier at high frequency, causing significant system slowdowns and potentially saturating the machine's resources.

The sys_membarrier system call is designed to provide memory ordering guarantees across multiple threads without requiring individual memory barriers in each thread. However, on some systems, this operation can be computationally expensive, and without rate limiting or access serialization, malicious or poorly written applications could abuse this to cause system-wide performance degradation.

Critical Impact

Local attackers with low privileges can exploit the unserialised sys_membarrier path to cause denial of service conditions by saturating system resources through rapid repeated invocations.

Affected Products

• Linux Kernel (multiple affected versions)
• Debian LTS distributions using affected kernel versions

Discovery Timeline

• February 26, 2024 - CVE-2024-26602 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-26602

Vulnerability Analysis

The vulnerability resides in the sched/membarrier subsystem of the Linux kernel. The sys_membarrier system call is used to issue memory barriers across all threads of a process, which is useful for implementing read-copy-update (RCU) patterns and other lock-free data structures. However, this operation can be very expensive on certain hardware architectures and system configurations.

The root issue is that the sys_membarrier code path lacked proper serialization controls, allowing it to be called at an arbitrarily high frequency. When invoked rapidly, the cumulative cost of these operations can overwhelm the system, leading to significant performance degradation affecting all running processes.

This vulnerability requires local access to exploit, meaning an attacker must have the ability to execute code on the target system. However, the privilege requirements are low—any unprivileged user can invoke the sys_membarrier syscall.

Root Cause

The root cause of this vulnerability is the absence of serialization mechanisms on the sys_membarrier code path. Without a lock or rate-limiting mechanism, concurrent or rapid sequential calls to sys_membarrier could consume excessive CPU resources and memory bandwidth, particularly on multi-processor systems where the memory barrier operations must propagate across all CPUs.

The fix introduces a lock on the sys_membarrier path to serialize access, preventing the ability for this system call to be invoked at too high a frequency and thus mitigating the potential for resource saturation.

Attack Vector

The attack vector for CVE-2024-26602 is local. An attacker with unprivileged access to a Linux system running a vulnerable kernel version can craft a simple program that repeatedly calls sys_membarrier in a tight loop. This does not require elevated privileges, as the membarrier() system call is accessible to normal user processes.

The attack could be executed as a straightforward denial of service, where the attacker's goal is to degrade system performance for all users. In a multi-tenant environment such as shared hosting or containerized workloads, this could allow one tenant to negatively impact others sharing the same kernel.

Detection Methods for CVE-2024-26602

Indicators of Compromise

• Unusual spike in sys_membarrier system call frequency from specific processes
• Processes exhibiting abnormally high CPU utilization without corresponding legitimate workload
• System-wide performance degradation without apparent cause
• Audit logs showing repeated membarrier() syscalls from unprivileged processes

Detection Strategies

• Monitor system call patterns using tools like strace, perf, or eBPF-based tracing to identify processes making excessive sys_membarrier calls
• Implement syscall auditing via the Linux audit subsystem to log membarrier() invocations and flag anomalous patterns
• Deploy endpoint detection solutions that can correlate process behavior with system resource utilization anomalies

Monitoring Recommendations

• Enable kernel syscall auditing for the membarrier syscall and establish baseline calling patterns
• Use SentinelOne's Singularity platform to monitor for behavioral anomalies indicative of resource exhaustion attacks
• Configure alerts for processes that exhibit sustained high syscall rates targeting memory barrier operations

How to Mitigate CVE-2024-26602

Immediate Actions Required

• Update the Linux kernel to a patched version that includes the serialization fix for sys_membarrier
• Review running processes for suspicious behavior patterns related to membarrier() syscall abuse
• Consider implementing resource limits (cgroups) to constrain the impact of potential abuse in multi-tenant environments
• Apply vendor-provided security updates from distribution maintainers (e.g., Debian LTS updates)

Patch Information

The Linux kernel maintainers have released patches that add serialization to the sys_membarrier path, preventing abuse through high-frequency invocations. Multiple commits have been backported to stable kernel branches:

• Kernel Git Commit 2441a64070b8
• Kernel Git Commit 24ec7504a08a
• Kernel Git Commit 3cd139875e9a
• Kernel Git Commit 50fb4e17df31

Debian LTS users should refer to the Debian LTS Security Announcements for distribution-specific update instructions.

Workarounds

• Implement syscall filtering using seccomp-bpf to restrict access to membarrier() for untrusted processes or containers
• Use cgroups CPU quotas to limit the resources available to potentially malicious processes
• In containerized environments, consider restricting the membarrier() syscall in container runtime security profiles
• Monitor and terminate processes exhibiting suspicious sys_membarrier abuse patterns

# Example: Using seccomp to restrict membarrier syscall in containers
# Add membarrier to blocked syscalls in container security profile
# For Docker, create a custom seccomp profile that denies membarrier
# Location: /etc/docker/seccomp/custom-profile.json
# Or apply resource limits via cgroups
systemctl set-property user-$UID.slice CPUQuota=50%