CVE-2026-63823 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
keys: Pin request_key_auth payload in instantiate paths
A: request_key() B: KEYCTL_INSTANTIATE_IOV ================ =========================
create auth key store rka in auth key wait for helper get auth key load rka from auth key copy user payload sleep on #PF
helper completed detach and free rka destroy auth key wake up use rka->target_key **USE-AFTER-FREE**
Give request_key_auth payloads a refcount. Take a payload reference while authkey->sem stabilizes the payload and revocation state. Hold that reference across the instantiate and reject paths. Drop the auth key owning reference from revoke and destroy.
[jarkko: Replaced the first two paragraphs of text with an actual
concurrency scenario.]
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/19/2026
This vulnerability resides in the Linux kernel's key management subsystem, specifically affecting the request_key() function when processing KEYCTL_INSTANTIATE_IOV operations. The flaw represents a classic use-after-free condition that occurs during the instantiation of authentication keys within concurrent execution contexts. The vulnerability manifests when multiple threads simultaneously access and manipulate authentication key data structures, creating race conditions that can lead to memory corruption and potential privilege escalation. This issue directly impacts the kernel's ability to maintain secure and consistent state management for cryptographic keys used in various security operations.
The technical root cause involves improper reference counting mechanisms within the key management framework where authentication key payloads lack adequate protection against premature deallocation. During the instantiation process, the system creates an authentication key store (rka) that undergoes a series of operations including waiting for helper completion, loading the authentication key, copying user payload data, and then sleeping on page fault handling. The vulnerability emerges when the helper function completes its execution, detaches and frees the rka structure, but subsequent code paths still attempt to reference the now-freed memory location. This race condition occurs because there is insufficient synchronization between the point where the authentication key is freed and where references to its payload might still be active.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling malicious actors to execute arbitrary code with kernel privileges. Attackers could exploit this condition by crafting specific sequences of key management operations that force the kernel into the vulnerable execution path, leading to privilege escalation or denial of service conditions. The vulnerability affects systems running Linux kernels where the key management subsystem is actively utilized for authentication and authorization purposes, making it particularly concerning for enterprise environments relying on kernel-level security features. This flaw aligns with CWE-416 which describes use-after-free vulnerabilities in software systems.
Mitigation strategies must focus on implementing proper reference counting mechanisms and synchronization primitives within the kernel's key management code. The solution involves granting request_key_auth payloads a proper refcount mechanism, taking payload references during authentication key semaphore stabilization, and maintaining those references across both instantiate and reject code paths. The fix requires holding references throughout the critical section where authentication key state is being modified and only dropping the reference after all potential access points have completed their operations. This approach directly addresses the concurrency issues identified in the vulnerability description by ensuring that payload memory remains valid for the duration of all active operations, preventing the use-after-free condition from occurring.
The remediation approach follows established security patterns recommended in various kernel security frameworks and aligns with ATT&CK technique T1068 which covers privilege escalation through local exploits. The fix essentially implements a proper reference counting strategy that prevents premature deallocation while maintaining performance characteristics of the key management subsystem. This solution ensures that the kernel's security model remains intact by preventing memory corruption that could be leveraged for unauthorized access to sensitive system resources. The implementation must be carefully tested to avoid introducing new race conditions or performance regressions in the already complex key management infrastructure.