Look up another CVE · open CVE-2026-89747 in the interactive tracker
CVE-2026-89747
tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem kernel/trace. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-89747 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Writing to buffer_subbuf_size_kb calls ring_buffer_subbuf_order_set(), which frees every sub-buffer of the ring buffer, including the reader page, and replaces them with newly allocated ones. Readers of trace_pipe hold pointers into those pages. ring_buffer_peek() looks up an event under cpu_buffer->reader_lock but returns the event pointer after dropping the lock, and peek_next_entry() then calls ring_buffer_event_length() and ring_buffer_event_data() on it. If the sub-buffer order is changed in that window, the reader dereferences freed memory: BUG: KASAN: use-after-free in ring_buffer_peek+0x3e0/0x430 Read of size 1 at addr ffff88802a4cf010 by task syz-executor989/6002 Freed by: free_buffer_page kernel/trace/ring_buffer.c:398 [inline] ring_buffer_subbuf_order_set+0x1325/0x18e0 kernel/trace/ring_buffer.c:7444 buffer_subbuf_size_write+0x182/0x280 kernel/trace/trace.c:8221 Take trace_access_lock(RING_BUFFER_ALL_CPUS) around the order change. This is the lock trace_pipe readers already hold across their entire peek-and-print loop, so the swap can no longer race with a reader that is dereferencing a peeked event.
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/trace/trace.c
- What this is
- TRACINGMAINTAINERS section matched on kernel/trace/ · linux-kernel@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_FUNCTION_TRACER|CONFIG_RETHOOK|CONFIG_RING_BUFFER|CONFIG_TRACEPOINTS|CONFIG_TRACE_CLOCK|CONFIG_TRACING' /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 arm64/arm64, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le
- trixieYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- forky, sidYnot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae
- bookworm · linux-6.12Ynot built on arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp
- Y
- built in where it is built at all; some flavours do not build it
- Build switches
- CONFIG_FUNCTION_TRACER, CONFIG_RETHOOK, CONFIG_RING_BUFFER, CONFIG_TRACEPOINTS, CONFIG_TRACE_CLOCK, CONFIG_TRACING
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-09-11 (37 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.2% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- kernel/trace
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.8 | 6.12.109 | 05ebe1e1d7d3 |
| 6.8 | 6.18.50 | ddbe921ed16a |
| 6.8 | 7.2.4 | 7a49d19ff9ba |
| 6.8 | 7.3 | 372f8534244d |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | 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:LAttack vector, local
- The UAF is reached only via local tracefs: write() to buffer_subbuf_size_kb (buffer_subbuf_size_write -> ring_buffer_subbuf_order_set) racing with read()/splice() of trace_pipe (tracing_read_pipe -> ring_buffer_peek). No network, adjacent-radio, or physical-device path reaches this code.
- AC:LAttack complexity, low
- The attacker controls both sides of the race: one thread reads trace_pipe while another writes buffer_subbuf_size_kb, which frees the reader page after dropping reader_lock. ring_buffer_peek then dereferences the stale event pointer; the attempt is retryable at will and CONFIG_TRACING is standard.
- PR:LPrivileges required, low
- tracing_check_open_get_tr() checks only LOCKDOWN_TRACEFS and DAC, with no capable() gate. buffer_subbuf_size_kb (0640) and trace_pipe (0440) are delegated via uid=/gid= mounts to tracing-group accounts on Android/Perfetto, ChromeOS, and developer systems, matching CVE-2025-38101 and CVE-2026-74634.
- UI:NUser interaction, none
- The attacker opens and reads their own trace_pipe and writes buffer_subbuf_size_kb from their own threads. No victim action, mount, or file open by another user is required.
- S:UScope, unchanged
- The use-after-free corrupts kernel ring-buffer pages and metadata inside the host kernel's security authority. It can yield local privilege escalation but does not cross a VM, IOMMU, container, or hardware trust boundary.
- C:HConfidentiality impact, high
- ring_buffer_subbuf_order_set() frees reader-page sub-buffers while ring_buffer_peek() still holds a pointer into them; peek_next_entry() and print_trace_line() then read the freed event and copy it to userspace via trace_pipe, disclosing recycled kernel heap contents.
- I:HIntegrity impact, high
- Freed sub-buffer pages and buffer_page objects can be reallocated while the reader still consumes attacker-controlled type_len/payload and print_trace_line() dispatches on iter->ent->type. This UAF heap corruption is exploitable for arbitrary kernel writes and control-flow hijack.
- A:HAvailability impact, high
- Dereferencing the freed reader page in ring_buffer_peek()/ring_buffer_event_length() causes a kernel oops, which is the syzbot KASAN use-after-free. The attacker can retrigger that crash at will.