# CVE-2026-98530: kprobes: Fix permanent hang when flushing the kprobe optimizer

> A local attacker with root privileges can cause a permanent system hang by disabling kprobes optimization while a probe is active.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98530, GHSA-2p4m-w3h2-4q6g, UBUNTU-CVE-2026-98530

## What is CVE-2026-98530?

CVE-2026-98530 is a denial of service vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

kprobes: Fix permanent hang when flushing the kprobe optimizer

Writing 0 to /proc/sys/debug/kprobes-optimization while a kprobe is
jump-optimized never returns. The writer sleeps in D state forever with
kprobe_sysctl_mutex held, so any later read or write of that sysctl
hangs as well. For example, with vfs_read+9 as an optimizable address
in this build:

  # cd /sys/kernel/tracing
  # echo 'p:myprobe vfs_read+9' >> kprobe_events
  # echo 1 > events/kprobes/myprobe/enable
  # # wait until /sys/kernel/debug/kprobes/list shows [OPTIMIZED]
  # echo 0 > /proc/sys/debug/kprobes-optimization

  INFO: task sh:246 blocked for more than 10 seconds.
  Call Trace:
   <TASK>
   __schedule+0x1176/0x4f70
   schedule+0xdc/0x2c0
   schedule_timeout+0x17b/0x260
   wait_for_completion+0x173/0x3c0
   wait_for_kprobe_optimizer_locked+0xbc/0x130
   proc_kprobes_optimization_handler+0x156/0x1b0
   proc_sys_call_handler+0x324/0x490
   vfs_write+0x52d/0xfe0
   ksys_write+0xff/0x200
   do_syscall_64+0x106/0x630
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>
  ...
  INFO: task cat:265 is blocked on a mutex likely owned by task sh:246.

wait_for_kprobe_optimizer_locked() reinitializes optimizer_completion,
asks the optimizer thread to flush and sleeps in wait_for_completion().
The thread drains the (un)optimizing lists, but calls complete() only
if completion_done() is true, i.e. if the completion is already done,
which never happens while someone waits. disarm_all_kprobes() and
kprobe_trace_self_tests_init() wait the same way.

Calling complete() unconditionally would not be enough: the waiter
drops kprobe_mutex while it sleeps, and nothing else serializes the
sysctl handler against the debugfs "enabled" file. A second flusher
that still finds the lists non-empty, e.g. because a disabled probe is
queued for unoptimizing, reinitializes the completion under the first:

  sysctl write                      debugfs "enabled" write
  unoptimize_all_kprobes()
    wait_for_kprobe_optimizer_locked()
      init_completion(c)
      mutex_unlock(&kprobe_mutex)
      wait_for_completion(c)
                                    disarm_all_kprobes()
                                      wait_for_kprobe_optimizer_locked()
                                        init_completion(c)
                                          // c->wait is reset, the first
                                          // waiter is off the queue
                                        mutex_unlock(&kprobe_mutex)
                                        wait_for_completion(c)
  kprobe_optimizer()
    complete(c)
      // wakes the debugfs writer only

where c is &optimizer_completion. Lining up the two writes during an
optimizer pass loses the sysctl writer this way.

Replace the completion with a counter of optimizer passes, bumped at the
end of each pass and signalled with wake_up_var_locked(), both under
kprobe_mutex. A flusher samples the count and waits with
wait_var_event_mutex(), which drops kprobe_mutex only while sleeping, so
a new count means a whole pass ran in the meantime. Nothing is
reinitialized, so several flushers can sleep in the wait at once.

## Which versions are affected by CVE-2026-98530?


## How do I fix CVE-2026-98530?

Apply the vendor's patch.

## Is CVE-2026-98530 being exploited?

There is no known exploitation of CVE-2026-98530 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98530 and fix it if it is affected.

What it is: CVE-2026-98530 is a denial of service vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98530 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98530/ (Markdown: https://insights.sbomify.com/CVE-2026-98530/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98530
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98530
- OSV: https://osv.dev/vulnerability/CVE-2026-98530

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98530/
Summaries are generated and may contain mistakes; the official description above is the record.