CVE-2026-23263: Linux Kernel Information Disclosure Flaw

CVE-2026-23263 Overview

A memory leak vulnerability has been identified in the Linux kernel's io_uring zero-copy receive (zcrx) subsystem. The issue stems from an incomplete fix in commit d9f595b9a65e which addressed page leakage on scatter-gather initialization failures. While that patch prevented individual pages from leaking, it failed to release the page array structure itself, resulting in a persistent memory leak that could impact system stability under repeated failure conditions.

Critical Impact

This memory leak vulnerability in the Linux kernel's io_uring/zcrx subsystem can lead to gradual memory exhaustion on systems that utilize zero-copy receive operations, potentially causing denial of service conditions.

Affected Products

• Linux kernel versions with io_uring/zcrx support
• Systems utilizing io_uring zero-copy receive functionality

Discovery Timeline

• 2026-03-18 - CVE CVE-2026-23263 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-23263

Vulnerability Analysis

This vulnerability is classified as a Memory Leak within the Linux kernel's io_uring subsystem, specifically in the zero-copy receive (zcrx) component. The io_uring interface provides high-performance asynchronous I/O capabilities, and the zero-copy receive feature is designed to minimize data copying overhead during network operations.

The root issue arose from an incomplete patch in commit d9f595b9a65e titled "io_uring/zcrx: fix leaking pages on sg init fail." While this earlier fix successfully addressed the leakage of individual pages when scatter-gather initialization failed, it overlooked the need to also free the page array structure that holds references to those pages.

In kernel programming, memory management requires careful attention to nested allocations. When a page array is allocated to hold multiple page references, both the individual pages and the array itself must be properly freed during error handling or cleanup routines. The failure to release the page array results in memory that remains allocated but unreachable, constituting a memory leak.

Root Cause

The vulnerability originates from incomplete error handling in the io_uring/zcrx code path. When scatter-gather initialization fails, the cleanup routine properly releases the individual pages but does not free the dynamically allocated page array structure. This oversight means that each failure event permanently consumes memory that cannot be reclaimed without a system restart.

Attack Vector

The attack vector is currently unknown pending further analysis. However, memory leak vulnerabilities in kernel subsystems typically require the ability to trigger the affected code path repeatedly. In this case, an attacker with the ability to cause repeated scatter-gather initialization failures in io_uring zero-copy receive operations could potentially exhaust system memory over time, leading to denial of service conditions.

The vulnerability is addressed by ensuring the page array is properly freed when releasing pages during error conditions. The fix adds the necessary deallocation call to the cleanup path, preventing memory accumulation during failure scenarios.

Detection Methods for CVE-2026-23263

Indicators of Compromise

• Gradual memory consumption increase on systems using io_uring zero-copy receive operations
• Kernel memory pool depletion without corresponding increase in application memory usage
• System instability or out-of-memory conditions on servers with heavy io_uring workloads

Detection Strategies

• Monitor kernel memory allocation statistics using tools like /proc/meminfo and /proc/slabinfo
• Implement memory leak detection using kernel debugging features such as KMEMLEAK
• Review io_uring operation failure rates in application logs

Monitoring Recommendations

• Configure alerts for unusual kernel memory consumption patterns
• Monitor systems utilizing io_uring for unexpected memory growth over time
• Implement regular memory auditing on production systems with io_uring workloads

How to Mitigate CVE-2026-23263

Immediate Actions Required

• Review systems for io_uring zero-copy receive usage and assess exposure
• Apply kernel patches from the official kernel git repository
• Plan maintenance windows for kernel updates on affected systems
• Consider temporarily disabling io_uring zero-copy receive functionality if memory issues are observed

Patch Information

Official patches have been released through the Linux kernel stable tree. The following commits address this vulnerability:

• Kernel Git Commit Changes - Commit 0ae91d8ab70922fb74c22c20bedcb69459579b1c
• Kernel Git Commit Updates - Commit 64cf3016234ce8a6e4195ed1b2d9e2a1ae41b57d

System administrators should update to the latest stable kernel version that includes these patches.

Workarounds

• Limit io_uring usage to trusted applications until patches can be applied
• Monitor memory consumption and schedule proactive reboots if memory leak symptoms are observed
• Consider alternative I/O mechanisms temporarily if zero-copy receive is not critical

Applying the official kernel patch is the recommended long-term solution. The patch ensures proper cleanup of the page array structure alongside the individual pages during scatter-gather initialization failures.