# CVE-2026-93167: csky: Fix a4/a5 restoration in syscall trace path

> A local attacker can cause denial of service by triggering corrupted syscall arguments in the C-SKY architecture trace path.

- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102876, BELL-CVE-2026-93167, DEBIAN-CVE-2026-93167, GHSA-fgg4-f5v2-253f, UBUNTU-CVE-2026-93167

## What is CVE-2026-93167?

CVE-2026-93167 is a vulnerability in Linux, published on 17 Sep 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:

csky: Fix a4/a5 restoration in syscall trace path

The syscall trace path reloads syscall arguments from pt_regs before
calling the syscall handler. On C-SKY ABIv2, the 5th and 6th syscall
arguments are prepared as stack arguments before invoking syscallid.

The current code adjusts sp before loading LSAVE_A4 and LSAVE_A5. Since
those offsets are relative to the original pt_regs base, loading them
after changing sp fetches the wrong slots. As a result, traced syscalls
that use the 5th or 6th argument may receive corrupted arguments.

This is visible with mmap2(), which takes six arguments. A small
PTRACE_SYSCALL reproducer opens a file and maps one page with:

  mmap(NULL, 4096, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0)

Before the fix, the traced child fails the mmap and exits with 12.
After the fix, the mapping succeeds and the child exits with 0.

Fix the trace path by loading a4/a5 from pt_regs before changing sp.

Tested on: ck860f, linux-4.19.15, C-SKY abiv2

## Which versions are affected by CVE-2026-93167?


## How do I fix CVE-2026-93167?

Apply the vendor's patch.

## Is CVE-2026-93167 being exploited?

There is no known exploitation of CVE-2026-93167 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93167 and fix it if it is affected.

What it is: CVE-2026-93167 is a vulnerability in Linux, published on 17 Sep 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-2026-93167 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-2026-93167/ (Markdown: https://insights.sbomify.com/CVE-2026-93167/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93167
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93167
- OSV: https://osv.dev/vulnerability/CVE-2026-93167

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93167/
Summaries are generated and may contain mistakes; the official description above is the record.