# CVE-2026-90339: powerpc/syscall: Fix syscall skip handling for seccomp and ptrace

> A flaw in the Linux kernel PowerPC syscall handling allows bypassing seccomp or ptrace restrictions, potentially enabling unauthorized system call execution.

- **Severity:** Not scored
- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-qfw2-5x2v-5xgv, UBUNTU-CVE-2026-90339

## What is CVE-2026-90339?

CVE-2026-90339 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:

powerpc/syscall: Fix syscall skip handling for seccomp and ptrace

After enabling GENERIC_ENTRY on PowerPC, syscall_enter_from_user_mode()
returns -1 as a sentinel to signal that seccomp or ptrace has intercepted
the syscall and already set a return value via syscall_set_return_value().
system_call_exception() was not handling this sentinel, and since -1UL
is >= NR_syscalls, the code fell into the out-of-range path and returned
-ENOSYS, overwriting the errno already placed in regs->gpr[3].

The naive fix of checking r0 == -1L before the NR_syscalls bounds check
is ambiguous: a user legitimately calling syscall(-1) also produces r0 ==
-1L, and a tracer intercepting such a call would have its injected return
value silently discarded.

Fix this by introducing a thread flag that is set whenever
syscall_set_return_value() explicitly updates the return value. In
system_call_exception(), check and clear this flag before dispatching
the syscall, and return the preset value directly when it is present.
This ensures that an explicitly supplied return value always suppresses
syscall execution, regardless of the syscall number.

This handles all seccomp actions correctly:

  - SECCOMP_RET_ERRNO, SECCOMP_RET_TRACE (no tracer), SECCOMP_RET_USER_NOTIF:
    all call syscall_set_return_value(), flag is set, injected value returned.
  - SECCOMP_RET_TRAP, SECCOMP_RET_KILL: call syscall_rollback() and deliver
    a signal; flag is not set, but the process is dying so the return value
    is irrelevant.

The fix covers both ppc32 and ppc64 with no #ifdefs.

## Which versions are affected by CVE-2026-90339?


## How do I fix CVE-2026-90339?

Apply the vendor's patch.

## Is CVE-2026-90339 being exploited?

There is no known exploitation of CVE-2026-90339 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90339 and fix it if it is affected.

What it is: CVE-2026-90339 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-2026-90339 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-2026-90339/ (Markdown: https://insights.sbomify.com/CVE-2026-90339/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90339
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90339
- OSV: https://osv.dev/vulnerability/CVE-2026-90339

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90339/
Summaries are generated and may contain mistakes; the official description above is the record.