CVE-2026-23066
Published: 04 February 2026
Summary
CVE-2026-23066 is a high-severity Uncontrolled Recursion (CWE-674) vulnerability in Linux Linux Kernel. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 6.8th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 RA-5 (Vulnerability Monitoring and Scanning) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-23066 is a vulnerability in the Linux kernel's RxRPC implementation, specifically within the rxrpc_recvmsg() function. When recvmsg() fails due to the MSG_DONTWAIT flag but the call at the front of the recvmsg queue has its mutex locked, the function unconditionally requeues the call, even if it is already queued—such as after a prior MSG_PEEK operation or requeue by the I/O thread. This behavior corrupts the recvmsg queue, potentially leading to use-after-free (UAF) conditions or reference count underruns. An additional issue with MSG_PEEK not dequeuing calls but incorrectly notifying the socket is also addressed.
A local attacker with low privileges (PR:L) can exploit this vulnerability with low attack complexity (AC:L) and no user interaction (UI:N) in an unprivileged scope (S:U). Successful exploitation could result in high impacts across confidentiality, integrity, and availability (C:H/I:H/A:H), with a CVSS v3.1 base score of 7.8. The attacker could leverage the queue corruption to trigger UAFs or refcount bugs, potentially enabling arbitrary code execution or kernel crashes.
Mitigation involves applying the upstream kernel patches provided in the referenced stable commits: 0464bf75590da75b8413c3e758c04647b4cdb3c6, 2c28769a51deb6022d7fbd499987e237a01dd63a, 930114425065f7ace6e0c0630fab4af75e059ea8, and cf969bddd6e69c5777fa89dc88402204e72f312a. These fixes ensure calls are only requeued if not already on the queue (moving them to the front if present), properly handle references on non-queued calls, and correct MSG_PEEK socket notifications when not all queue data is consumed. Security practitioners should update affected Linux kernels to versions incorporating these commits.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-5478
Vulnerability details
In the Linux kernel, the following vulnerability has been resolved: rxrpc: Fix recvmsg() unconditional requeue If rxrpc_recvmsg() fails because MSG_DONTWAIT was specified but the call at the front of the recvmsg queue already has its mutex locked, it requeues the…
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call - whether or not the call is already queued. The call may be on the queue because MSG_PEEK was also passed and so the call was not dequeued or because the I/O thread requeued it. The unconditional requeue may then corrupt the recvmsg queue, leading to things like UAFs or refcount underruns. Fix this by only requeuing the call if it isn't already on the queue - and moving it to the front if it is already queued. If we don't queue it, we have to put the ref we obtained by dequeuing it. Also, MSG_PEEK doesn't dequeue the call so shouldn't call rxrpc_notify_socket() for the call if we didn't use up all the data on the queue, so fix that also.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Local kernel UAF/refcount bug in RxRPC directly enables unprivileged local attackers to achieve arbitrary code execution or kernel-level compromise, mapping to exploitation for privilege escalation.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely remediation of kernel flaws like CVE-2026-23066 through patching to eliminate recvmsg queue corruption and prevent UAF or refcount underruns.
Vulnerability scanning identifies the presence of CVE-2026-23066 in Linux kernels, enabling prioritization and remediation of the RxRPC recvmsg bug.
Kernel memory protection mechanisms mitigate the impact of use-after-free conditions arising from the corrupted recvmsg queue in RxRPC.