# CVE-2026-52906: 9p: fix access mode flags being ORed instead of replaced

> A logic error in the Linux kernel 9p filesystem causes root to lose privileged capabilities, potentially allowing privilege escalation or denial of service.

- **Severity:** High 7.7 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Jun 2026
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-52906, GHSA-4vm9-m655-vqf4, UBUNTU-CVE-2026-52906

## What is CVE-2026-52906?

CVE-2026-52906 is a high-severity vulnerability in Linux kernel, published on 9 Jun 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:

9p: fix access mode flags being ORed instead of replaced

Since commit 1f3e4142c0eb ("9p: convert to the new mount API"),
v9fs_apply_options() applies parsed mount flags with |= onto flags
already set by v9fs_session_init(). For 9P2000.L, session_init sets
V9FS_ACCESS_CLIENT as the default, so when the user mounts with
"access=user", both bits end up set. Access mode checks compare
against exact values, so having both bits set matches neither mode.

This causes v9fs_fid_lookup() to fall through to the default switch
case, using INVALID_UID (nobody/65534) instead of current_fsuid()
for all fid lookups. Root is then unable to chown or perform other
privileged operations.

Fix by clearing the access mask before applying the user's choice.

## Which versions are affected by CVE-2026-52906?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52906?

Apply the vendor's patch.

## Is CVE-2026-52906 being exploited?

There is no known exploitation of CVE-2026-52906 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-2026-52906 and fix it if it is affected.

What it is: CVE-2026-52906 is a high-severity vulnerability in Linux kernel, published on 9 Jun 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-2026-52906 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-2026-52906/ (Markdown: https://insights.sbomify.com/CVE-2026-52906/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52906
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52906
- OSV: https://osv.dev/vulnerability/CVE-2026-52906

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52906/
Summaries are generated and may contain mistakes; the official description above is the record.