Linux kernel rt_mutex remove_waiter() UAF vulnerability
CVE-2026-43499 Published on May 21, 2026
rtmutex: Use waiter::task instead of current in remove_waiter()
In the Linux kernel, the following vulnerability has been resolved:
rtmutex: Use waiter::task instead of current in remove_waiter()
remove_waiter() is used by the slowlock paths, but it is also used for
proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from
futex_requeue().
In the latter case waiter::task is not current, but remove_waiter()
operates on current for the dequeue operation. That results in several
problems:
1) the rbtree dequeue happens without waiter::task::pi_lock being held
2) the waiter task's pi_blocked_on state is not cleared, which leaves a
dangling pointer primed for UAF around.
3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter
task
Use waiter::task instead of current in all related operations in
remove_waiter() to cure those problems.
[ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the
changelog ]
Products Associated with CVE-2026-43499
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Affected Versions
Linux:- Version 8161239a8bcce9ad6b537c04a1fa3b5c68bae693 and below 8a1fc8d698ac5e5916e3082a0f74450d71f9611f is affected.
- Version 8161239a8bcce9ad6b537c04a1fa3b5c68bae693 and below 6d52dfcb2a5db86e346cf51f8fcf2071b8085166 is affected.
- Version 8161239a8bcce9ad6b537c04a1fa3b5c68bae693 and below 3fb7394a837740770f0d6b4b30567e60786a63f2 is affected.
- Version 8161239a8bcce9ad6b537c04a1fa3b5c68bae693 and below 88614876370aac8ad1050ad785a4c095ba17ac11 is affected.
- Version 8161239a8bcce9ad6b537c04a1fa3b5c68bae693 and below 3bfdc63936dd4773109b7b8c280c0f3b5ae7d349 is affected.
- Version 2.6.39 is affected.
- Before 2.6.39 is unaffected.
- Version 6.6.140, <= 6.6.* is unaffected.
- Version 6.12.86, <= 6.12.* is unaffected.
- Version 6.18.27, <= 6.18.* is unaffected.
- Version 7.0.4, <= 7.0.* is unaffected.
- Version 7.1-rc1, <= * is unaffected.