CVE-2026-93191 smack: fix incorrect task context in smack_msg_queue_msgrcv
A flaw in the Linux kernel SMACK module allows unauthorized local users to read messages from System V message queues, bypassing Mandatory Access Control policies.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-93191?
CVE-2026-93191 is a vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smack: fix incorrect task context in smack_msg_queue_msgrcv
The smack_msg_queue_msgrcv() function incorrectly checks the permissions of the 'current' task instead of the 'target' task.
In the msgsnd() syscall path, if a receiver is already waiting, the pipelined_send() optimization is used to push the message directly to the receiver task:
ipc/msg.c`pipelined_send(): ` smp_store_release(&msr->r_msg, msg)
In this case, the 'sender' (current) task performs the check on behalf of the 'receiver' task (msr->r_tsk, passed as the 'target' parameter):
ipc/msg.c`pipelined_send(): ` security_msg_queue_msgrcv(,, target := msr->r_tsk,,)
However, smack_msg_queue_msgrcv() ignores the 'target' and checks 'current':
smack_msg_queue_msgrcv(…) ` smk_curacc_msq(isp, MAY_READWRITE); // current task
'current' MAY satisfy smack_msg_queue_msgrcv r/w requirement, but 'target' (the receiver task) might NOT; as a result, an unauthorized receiver gets the message, violating MAC policy.
Test: 1) create a sysv message queue with label “foo” 2) echo "bar foo r" >/smack/load2 3) msgrcv(,,,0,MSG_NOERROR) in "bar"-labeled task. The task is waiting for the messages ... 4) msgsnd() from a "foo"-labeled task: "bar"-labeled task gets the message.
This patch fixes the issue by checking permission on the 'target' task instead of 'current'.
(2008-02-04, Casey Schaufler)
Which versions are affected by CVE-2026-93191?
How do I fix CVE-2026-93191?
Apply the vendor's patch.
Is CVE-2026-93191 being exploited?
There is no known exploitation of CVE-2026-93191 in the wild and no public exploit code.
Sources
Also known as AZL-102807, BELL-CVE-2026-93191, DEBIAN-CVE-2026-93191, GHSA-9697-g343-86c8, UBUNTU-CVE-2026-93191.