CVE-2026-23239 in Linux
Summary
by MITRE • 03/10/2026
In the Linux kernel, the following vulnerability has been resolved:
espintcp: Fix race condition in espintcp_close()
This issue was discovered during a code audit.
After cancel_work_sync() is called from espintcp_close(), espintcp_tx_work() can still be scheduled from paths such as the Delayed ACK handler or ksoftirqd. As a result, the espintcp_tx_work() worker may dereference a freed espintcp ctx or sk.
The following is a simple race scenario:
cpu0 cpu1
espintcp_close() cancel_work_sync(&ctx->work); espintcp_write_space() schedule_work(&ctx->work);
To prevent this race condition, cancel_work_sync() is replaced with disable_work_sync().
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability described in CVE-2026-23239 represents a critical race condition within the Linux kernel's espintcp implementation that affects the espintcp_close() function. This issue manifests as a timing window where memory management operations can lead to use-after-free conditions, potentially compromising system stability and security. The vulnerability was identified through systematic code auditing processes, highlighting the importance of thorough security reviews in kernel space components. The espintcp module serves as an interface for handling TCP connections in certain network contexts, making this flaw particularly concerning for network security and system integrity.
The technical flaw occurs in the sequence of operations within the espintcp_close() function where the kernel attempts to synchronize work cancellation but fails to prevent all potential scheduling paths. Specifically, after cancel_work_sync() is invoked to terminate pending work items, the espintcp_tx_work() worker function can still be scheduled through alternative code paths including the Delayed ACK handler and ksoftirqd processing threads. This creates a scenario where the worker function may attempt to access memory locations that have already been freed, resulting in undefined behavior and potential system crashes. The race condition is particularly subtle because it involves multiple execution contexts and timing dependencies that are difficult to reproduce in testing environments.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation or denial of service attacks. When the espintcp_tx_work() function executes against a freed context structure, it can cause memory corruption that may be exploited by malicious actors to execute arbitrary code with kernel privileges. The vulnerability affects the kernel's ability to properly manage TCP connection lifecycle operations, potentially leading to network service disruption and compromised system security. This type of race condition can be particularly dangerous in server environments where network connectivity is critical and system reliability is paramount. The issue demonstrates how seemingly minor synchronization problems in kernel code can have significant security implications.
The fix implemented addresses this race condition by replacing cancel_work_sync() with disable_work_sync() which provides stronger guarantees against work item scheduling after the cancellation operation. This change ensures that no new instances of espintcp_tx_work() can be scheduled once the close operation begins, preventing the use-after-free scenario. The solution aligns with established kernel development practices for handling work queue synchronization and follows the principles outlined in the Common Weakness Enumeration standard CWE-362 which catalogs concurrency weaknesses. The mitigation approach also reflects techniques commonly recommended in the MITRE ATT&CK framework for kernel-level security hardening, particularly in the area of privilege escalation prevention and system stability maintenance. This fix demonstrates the importance of comprehensive synchronization mechanisms in kernel space programming and the necessity of considering all potential code paths during security analysis.