CVE-2026-23259 Overview
A memory leak vulnerability has been discovered in the Linux kernel's io_uring subsystem, specifically within the read/write cleanup handling mechanism. The vulnerability occurs when a read/write request goes through io_req_rw_cleanup() with an allocated iovec attached and fails to put to the rw_cache, resulting in an unaccounted iovec pointer.
Critical Impact
This vulnerability may lead to memory leaks in the Linux kernel's io_uring subsystem, potentially causing resource exhaustion and system instability over time.
Affected Products
- Linux kernel with io_uring support
- Systems utilizing io_uring for asynchronous I/O operations
- Kernel versions prior to the security patch
Discovery Timeline
- 2026-03-18 - CVE CVE-2026-23259 published to NVD
- 2026-03-19 - Last updated in NVD database
Technical Details for CVE-2026-23259
Vulnerability Analysis
This vulnerability exists in the io_uring subsystem's handling of read/write request cleanup operations. The io_uring interface is a high-performance asynchronous I/O mechanism in the Linux kernel, designed to reduce system call overhead for I/O operations. The vulnerability manifests when the io_req_rw_cleanup() function processes a request that has an allocated iovec (I/O vector) structure attached to it.
When such a request fails to be placed into the rw_cache for recycling, the allocated iovec pointer becomes unaccounted for. This results in memory not being properly freed, leading to a memory leak condition. Over time, repeated triggering of this condition could exhaust kernel memory resources.
Root Cause
The root cause of this vulnerability lies in the inadequate error handling within the io_rw_recycle() function. When recycling a read/write request fails, the function did not properly communicate this failure to the caller, which meant that the associated iovec allocation was not freed. The fix modifies io_rw_recycle() to return a boolean indicating whether the request was successfully recycled, allowing the caller to determine whether to free the iovec allocation.
Attack Vector
The attack vector for this vulnerability requires local access to a system with io_uring capabilities. An attacker would need to perform specific sequences of read/write operations through the io_uring interface that trigger the cache put failure condition. While this vulnerability primarily results in a memory leak rather than code execution, sustained exploitation could lead to denial of service through resource exhaustion.
The vulnerability can be triggered through normal io_uring operations when the internal request cache reaches its limits or encounters other failure conditions that prevent successful recycling of requests.
Detection Methods for CVE-2026-23259
Indicators of Compromise
- Unusual kernel memory consumption growth over time without corresponding workload increases
- io_uring-related memory allocation errors in kernel logs
- System performance degradation in applications heavily utilizing io_uring
Detection Strategies
- Monitor kernel memory usage patterns for abnormal growth in io_uring-related allocations
- Implement kernel memory leak detection tools such as kmemleak to identify unfreed iovec structures
- Review system logs for io_uring subsystem warnings or errors related to cache operations
Monitoring Recommendations
- Enable kernel memory tracking and set alerts for unusual memory consumption patterns
- Monitor /proc/meminfo and /proc/slabinfo for signs of memory leaks in kernel data structures
- Deploy endpoint detection solutions capable of monitoring kernel-level memory anomalies
How to Mitigate CVE-2026-23259
Immediate Actions Required
- Update the Linux kernel to a patched version containing the security fix
- Consider temporarily disabling io_uring functionality on systems where it is not essential
- Monitor affected systems for signs of memory exhaustion
Patch Information
The vulnerability has been addressed in the Linux kernel through commits that modify the io_rw_recycle() function to properly return whether recycling succeeded. This allows the calling code to properly free the iovec allocation when cache placement fails.
Security patches are available through the official kernel git repository:
Workarounds
- Disable io_uring functionality via sysctl if not required for application operations
- Implement resource limits to prevent runaway memory consumption
- Schedule regular system reboots as a temporary measure to clear accumulated leaked memory
# Disable io_uring (if not needed)
echo 0 > /proc/sys/kernel/io_uring_disabled
# Alternative: Restrict io_uring to privileged users only
echo 2 > /proc/sys/kernel/io_uring_disabled
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
