EUVD-2026-39254
GHSA-4w7w-2mrj-36vw
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Local unprivileged futex invocation (AV:L, PR:L) causes kernel NULL dereference crash; no confidentiality or integrity impact, scope unchanged.
Primary rating from NVD.
CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
5DescriptionNVD
In the Linux kernel, the following vulnerability has been resolved:
locking/rtmutex: Skip remove_waiter() when waiter is not enqueued
syzbot triggered the following splat in remove_waiter() via FUTEX_CMP_REQUEUE_PI:
KASAN: null-ptr-deref in range [0x0000000000000a88-0x0000000000000a8f] class_raw_spinlock_constructor remove_waiter+0x159/0x1200 kernel/locking/rtmutex.c:1561 rt_mutex_start_proxy_lock+0x103/0x120 futex_requeue+0x10e4/0x20d0 __x64_sys_futex+0x34f/0x4d0
task_blocks_on_rt_mutex() does not arm the waiter upon deadlock detection, leaving waiter->task nil, where 3bfdc63936dd ("rtmutex: Use waiter::task instead of current in remove_waiter()") made this fatal.
Furthermore, rt_mutex_start_proxy_lock() should not be calling into remove_waiter() upon a successfully grabbing the rtmutex. 1a1fb985f2e2 ("futex: Handle early deadlock return correctly"), moved the remove_waiter() out of __rt_mutex_start_proxy_lock() (where 'ret' was only ever 0 or < 0) into the wrapper. Tighten this check to account for try_to_take_rt_mutex().
AnalysisAI
Null pointer dereference in the Linux kernel's real-time mutex (rtmutex) subsystem allows a local low-privileged user to crash the kernel via FUTEX_CMP_REQUEUE_PI, causing a denial of service. Affected stable branches span Linux 6.1 through 7.1-rc5; vendor patches are available via kernel.org stable commits. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a local user account with the ability to invoke the futex(2) syscall using the FUTEX_CMP_REQUEUE_PI command (operation value 12), which is available to unprivileged users in standard Linux distributions without seccomp restrictions. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 5.5 (Medium) correctly reflects the constrained threat model: local access only (AV:L), low privilege (PR:L), and a pure availability impact (A:H, C:N, I:N). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A local user on a multi-tenant system (shared server, container host with untrusted workloads, or CI runner) invokes FUTEX_CMP_REQUEUE_PI with futex addresses crafted to trigger the deadlock detection branch in task_blocks_on_rt_mutex(), which returns without initializing waiter->task. The subsequent remove_waiter() call dereferences the NULL waiter->task pointer, causing a kernel panic and crashing the host - denying service to all co-located tenants. … |
| Remediation | Apply the vendor-released stable kernel patches available from kernel.org. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-476 – NULL Pointer Dereference
View allSame technique Denial Of Service
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External POC / Exploit Code
Leaving vuln.today