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CVE-2026-72069
locking/rt: Fix the incorrect RCU protection in rt_spin_unlock()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem kernel/locking. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72069 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
kernel/locking/spinlock_rt.c
- What this is
- LOCKING PRIMITIVESMAINTAINERS section matched on kernel/locking/ · linux-kernel@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_PREEMPT_RT /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormYnot built on amd64/amd64, amd64/cloud-amd64, arm64/arm64, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, i386/686, i386/686-pae, ppc64el/powerpc64le
- trixieYnot built on amd64/amd64, amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- forky, sidYnot built on amd64/amd64, amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64, s390x/s390x
- bookworm · linux-6.12Ynot built on amd64/amd64, amd64/cloud-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, armhf/armmp, armhf/armmp-lpae, ppc64el/powerpc64le, ppc64el/powerpc64le-64k
- Y
- built in where it is built at all; some flavours do not build it
- Build switch
- CONFIG_PREEMPT_RT
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.73%, higher than 53.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- kernel/locking
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15 | 5.15.217 | af28d801cd2d |
| 5.15 | 6.1.184 | 9d1fcd64ab81 |
| 5.15 | 6.6.148 | 3cfaac77b3c3 |
| 5.15 | 6.12.101 | 1f0d56d3f1e8 |
| 5.15 | 6.18.40 | 633cadbc0b83 |
| 5.15 | 7.1.5 | 83f9fb561c1c |
| 5.15 | 7.2 | 89038cc87d80 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- On CONFIG_PREEMPT_RT, every spin_unlock() is substituted by rt_spin_unlock(); network subsystems such as netfilter xt_hashlimit process inbound packets through hashlimit_mt_common(), spin_lock/unlock on RCU-protected dsthash_ent objects concurrently freed via call_rcu by GC—the exact embedded-spinlock UAF pattern from the fix.
- AC:LAttack complexity, low
- The bug is a cross-CPU race where rt_spin_unlock() calls rcu_read_unlock() before releasing the rtmutex, ending the RCU grace period while still dereferencing the lock; syzbot triggered this reliably on PREEMPT_RT via concurrent unlinkat and dentry teardown, and attackers control both sides with parallel syscalls or packet/GC load.
- PR:NPrivileges required, none
- Remote attackers need no account, capability, or authentication to send packets that hit deployed hashlimit rules on internet-facing PREEMPT_RT gateways; the proven syzbot unlinkat path needs only directory write permission (PR:L), but PR:N reflects the highest-severity unauthenticated network packet scenario.
- UI:NUser interaction, none
- No victim interaction is required; the attacker drives the race through their own concurrent filesystem syscalls (syzbot: unlinkat racing __fput/dentry_kill) or sustained inbound traffic overlapping netfilter GC, without needing another user to open files or mount filesystems.
- S:UScope, unchanged
- The UAF corrupts kernel slab memory containing embedded spinlock/rtmutex fields and enables privilege escalation within the same kernel security authority; it does not inherently cross VM/guest, container sandbox, or IOMMU hardware isolation boundaries.
- C:HConfidentiality impact, high
- Syzbot reported KASAN slab-use-after-free Read in rt_mutex_slowunlock during spin_unlock on a freed dentry in shrink_dcache_tree; the systemic UAF lets attackers read freed objects (dentry, dsthash_ent, etc.) after premature RCU grace-period completion, enabling kernel pointer and memory disclosure.
- I:HIntegrity impact, high
- UAF on embedded rtmutex fields inside freed slab objects (dentry->d_lock per syzbot) permits heap grooming and reallocation of attacker-controlled data, providing standard kernel heap corruption primitives for arbitrary write and control-flow hijack beyond the immediate crash.
- A:HAvailability impact, high
- Syzbot hit KASAN slab-use-after-free causing kernel fault in shrink_dcache_tree via rt_spin_unlock on PREEMPT_RT; the bug can oops/panic any RT kernel whenever spin_unlock races RCU-deferred free of the containing object, enabling repeatable denial of service via concurrent VFS or netfilter operations.