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CVE-2026-74637
perf/core: Fix group leader use-after-free after sibling detach
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem kernel/events. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74637 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 | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
perf_group_detach() handles leader and sibling detach differently. When the group leader is detached, all siblings are promoted to singleton events and their group_leader pointer is reset to themselves. When a sibling is detached, it is removed from the leader's sibling_list, but its group_leader pointer is left pointing at the old leader. That is harmless when the sibling is being closed and freed immediately, as in the DETACH_DEAD path. It is not safe when the sibling is detached but kept alive, such as during CPU hotplug with DETACH_GROUP. In that case the sibling is removed from the context, while its file descriptor can still keep it alive. A typical failing sequence is: - A group contains leader L and sibling S. - CPU hot-unplug detaches S with DETACH_GROUP, removing it from L->sibling_list but leaving S->group_leader == L. - L is later closed and freed. - A PERF_IOC_FLAG_GROUP ioctl on S follows S->group_leader and dereferences the freed leader. This was reproduced by running the perf event fuzzer, CPU hotplug, and a stress workload concurrently: Unable to handle kernel paging request at virtual address 006b6b6b6b6b6cdb CPU: 2 PID: 12489 Comm: perf_fuzzer 6.18.7 PREEMPT pc : perf_ioctl+0x34c/0xc68 x20: ffffff89a3fa2c70 x8 : 6b6b6b6b6b6b6b6b Code: 943c4a0e 340047a0 f9404a94 f9411e88 (f940b908) Call trace: perf_ioctl+0x34c/0xc68 (P) __arm64_sys_ioctl+0xa0/0xf4 invoke_syscall+0x58/0xe4 el0_svc_common+0xa8/0xdc do_el0_svc+0x1c/0x28 el0_svc+0x40/0xc0 el0t_64_sync_handler+0x68/0xdc el0t_64_sync+0x1c4/0x1c8 The fault happened in perf_ioctl(), where perf_event_for_each() follows the stale group_leader pointer and perf_event_for_each_child() then dereferences the freed leader's context. Fix the use-after-free by promoting the detached sibling to a singleton. Also fix __event_disable() cgroup accounting and event state change.
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/events/core.c
- What this is
- PERFORMANCE EVENTS SUBSYSTEMMAINTAINERS section matched on kernel/events/* · linux-perf-users@vger.kernel.org · Supported
Check it on the machine
grep -w CONFIG_PERF_EVENTS /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 code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sid, bookworm · linux-6.12y
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_PERF_EVENTS
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
- 2026-08-22 (2 months 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
- 0.13%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- kernel/events
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.35 | 5.10.267 | 8f867c0e8da4 |
| 2.6.35 | 5.15.218 | 8e92e0398436 |
| 2.6.35 | 6.1.185 | f8a07021679a |
| 2.6.35 | 6.6.154 | 80c6054a4c40 |
| 2.6.35 | 6.12.105 | b42948f9e0d1 |
| 2.6.35 | 6.18.45 | a979a642402d |
| 2.6.35 | 7.1.9 | 1e7abfeb23c1 |
| 2.6.35 | 7.2 | 42c5ca1f0a28 |
| 2.6.34.14 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 bug is reached only through local perf_event_open(2), ioctl(2) on perf fds (PERF_IOC_FLAG_GROUP), close(2), and execve(2); perf_ioctl() follows the stale group_leader into freed memory. There is no network, adjacent-wireless, or physical device entry path.
- AC:LAttack complexity, low
- An attacker fully controls creation of leader/sibling groups, triggering sibling DETACH_GROUP via remove_on_exec or racing CPU hot-unplug against leader close, then issuing GROUP ioctls on the surviving sibling fd. The reproducer used perf_fuzzer with concurrent hotplug, and the attacker controls both sides of the lifecycle race.
- PR:LPrivileges required, low
- A basic unprivileged local user can open per-task perf event groups on their own process with exclude_kernel=1 under the default sysctl_perf_event_paranoid=2, without CAP_PERFMON or init-namespace root. security_perf_event_open(PERF_SECURITY_OPEN) and perf_check_permission() allow this self-monitoring path.
- UI:NUser interaction, none
- Exploitation requires no action from another user or administrator beyond the attacker running their own syscalls (open group, exec or wait for hotplug, close leader, ioctl sibling). No victim must mount filesystems, open files, or interact with the system.
- S:UScope, unchanged
- Impact is confined to kernel perf/core heap corruption and privilege escalation within the same host kernel security authority. This is not a VM escape, IOMMU bypass, or cross-namespace boundary change; it is standard local kernel memory corruption.
- C:HConfidentiality impact, high
- This is a use-after-free: perf_event_for_each() and perf_event_for_each_child() dereference a freed group leader and its context (repro showed 0x6b6b6b6b6b6b6b poisoned pointers). UAF on attacker-influenceable perf_event objects enables arbitrary kernel memory disclosure via controlled reallocations.
- I:HIntegrity impact, high
- Freed perf_event/group_leader structures can be reallocated with attacker-controlled data, providing heap grooming primitives for arbitrary kernel writes and control-flow hijack. Memory corruption from following stale group_leader pointers is exploitable beyond a simple crash.
- A:HAvailability impact, high
- The fix commit documents a reproducible kernel paging fault in perf_ioctl() ("Unable to handle kernel paging request"). UAF dereferences reliably cause kernel oops/panic or hang, giving full denial of service and potential system-wide unavailability on affected hosts.