# CVE-2026-64451: tracing: Fix NULL pointer dereference in func_set_flag()

> A local attacker can crash the Linux kernel by writing to a function tracer option file after switching the active tracer, causing a NULL pointer dereference.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-64451, GHSA-xvp7-xr44-89mj, ROOT-OS-UBUNTU-2204-CVE-2026-64451, UBUNTU-CVE-2026-64451

## What is CVE-2026-64451?

CVE-2026-64451 is a medium-severity vulnerability in Linux kernel, published on 25 Jul 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:

tracing: Fix NULL pointer dereference in func_set_flag()

func_set_flag() dereferences tr->current_trace_flags before verifying
that the current tracer is actually the function tracer. When the active
tracer has been switched away from "function" (e.g., to "wakeup_rt"),
tr->current_trace_flags can be NULL, leading to a NULL pointer
dereference and kernel crash.

The call chain that triggers this is:

  trace_options_write()
    -> __set_tracer_option()
      -> trace->set_flag()          /* func_set_flag */

In func_set_flag(), the first operation is:

  if (!!set == !!(tr->current_trace_flags->val & bit))

This dereferences tr->current_trace_flags unconditionally. The safety
check that guards against a non-function tracer:

  if (tr->current_trace != &function_trace)
      return 0;

is placed *after* the dereference, which is too late.

This was observed with the following crash dump:

  BUG: unable to handle page fault at 0000000000000000
  RIP: func_set_flag+0xd

  Call Trace:
   __set_tracer_option+0x27
   trace_options_write+0x75
   vfs_write+0x12a
   ksys_write+0x66
   do_syscall_64+0x5b

  RIP: ffffffff914c973d  RSP: ff67ec88b01dfdf0  RFLAGS: 00010202
  RAX: 0000000000000000  RBX: ff3a826e80354580  RCX: 0000000000000001
  RDX: 0000000000000001  RSI: 0000000000000000  RDI: ffffffff93918080

The disassembly confirms the fault:

  func_set_flag+0:   mov 0x1f08(%rdi), %rax  ; RAX = tr->current_trace_flags = NULL
  func_set_flag+13:  mov (%rax), %eax        ; page fault: dereference NULL

At the time of the crash:
  tr->current_trace_flags = 0x0 (NULL)
  tr->current_trace = wakeup_rt_tracer (not function_trace)

The scenario is that a process opens a function tracer option file (such
as "func_stack_trace"), then the current tracer is switched to another
tracer (e.g., "wakeup_rt"), which sets current_trace_flags to NULL. When
the process subsequently writes to the option file, func_set_flag() is
invoked and crashes on the NULL dereference.

Fix this by moving the current_trace check before the
current_trace_flags dereference, so that func_set_flag() returns early
when the function tracer is not active.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-64451?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64451?

Apply the vendor's patch.

## Is CVE-2026-64451 being exploited?

There is no known exploitation of CVE-2026-64451 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64451 and fix it if it is affected.

What it is: CVE-2026-64451 is a medium-severity vulnerability in Linux kernel, published on 25 Jul 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-2026-64451 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-64451/ (Markdown: https://insights.sbomify.com/CVE-2026-64451/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64451
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64451
- OSV: https://osv.dev/vulnerability/CVE-2026-64451

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64451/
Summaries are generated and may contain mistakes; the official description above is the record.