# CVE-2026-68186: binfmt_misc: set have_execfd only once the interpreter is opened

> Unprivileged users can trigger a kernel NULL pointer dereference in binfmt_misc by manipulating FUSE mounts, causing a local denial of service.

- **Severity:** Not scored
- **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:** 10 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** BELL-CVE-2026-68186, DEBIAN-CVE-2026-68186, GHSA-2h9p-pp39-9929, UBUNTU-CVE-2026-68186

## What is CVE-2026-68186?

CVE-2026-68186 is a vulnerability in Linux, published on 10 Aug 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:

binfmt_misc: set have_execfd only once the interpreter is opened

load_misc_binary() raises bprm->have_execfd as soon as it sees the 'O'
(or 'C') flag. This happens well before it opens the interpreter. If
that open fails the flag stays set on the bprm. binfmt_misc is at the
head of the format list so an interpreter open failure that returns
-ENOEXEC lets the search fall through to a later format. This means it
runs the matched binary directly having never staged an interpreter. So
bprm->executable is NULL while have_execfd falsely claims a descriptor
is present.

Consequently, begin_new_exec() dereferences the missing executable:

  would_dump(bprm, bprm->executable);

and NULL derefs. Had it not, the hand-off later in the same function
would have failed anyway. FD_ADD(0, bprm->executable) rejects a NULL
file with -ENOMEM. Both sites are past the point of no return so the
exec cannot be unwound either way.

This can be reached by unprivileged users as binfmt_misc can be mounted
in user namespaces. So a user can register an 'O' entry whose
interpreter lives on a FUSE mount, have the FUSE server fail the open
with -ENOEXEC and execute a native ELF file that matches the entry.

have_execfd only means anything alongside the executable it describes
which is not set until the interpreter has been opened and staged.
So lets raise it there, next to execfd_creds, which is already set at
that point. An open failure now leaves it clear, so the fallback format
derives credentials from the binary and emits no AT_EXECFD, as it would
for any native exec. The argv rewrite load_misc_binary() performs before
the open is still not undone. This means the binary sees the interpreter
path in argv[0] and its own path in argv[1] but that predates this
change and only became observable once the exec stopped faulting.

## Which versions are affected by CVE-2026-68186?


## How do I fix CVE-2026-68186?

Apply the vendor's patch.

## Is CVE-2026-68186 being exploited?

There is no known exploitation of CVE-2026-68186 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-68186 and fix it if it is affected.

What it is: CVE-2026-68186 is a vulnerability in Linux, published on 10 Aug 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-2026-68186 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-2026-68186/ (Markdown: https://insights.sbomify.com/CVE-2026-68186/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-68186
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-68186
- OSV: https://osv.dev/vulnerability/CVE-2026-68186

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-68186/
Summaries are generated and may contain mistakes; the official description above is the record.