# CVE-2026-54777: CoreWCF NetNamedPipe transport accepts attach to a pre-existing named pipe instance

> Local attackers can intercept NetNamedPipe traffic by racing service startup, exposing sensitive data in CoreWCF applications.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:L`)
- **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:** 8 Jul 2026
- **Updated:** 10 Jul 2026
- **Also known as:** GHSA-6jj2-4q5c-x8g6

## What is CVE-2026-54777?

CVE-2026-54777 is a medium-severity vulnerability in CoreWCF, published on 8 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

CoreWCF is a port of the service side of Windows Communication Foundation (WCF) to .NET Core. Prior to 1.8.1 and 1.9.1, CoreWCF NetNamedPipe transport accepts attachment to a pre-existing named pipe instance, allowing local interception of NetNamedPipe traffic when an attacker races NamedPipeListener startup between shared memory GUID publication and service named pipe creation. This issue is fixed in versions 1.8.1 and 1.9.1.

Weakness: CWE-665 (Improper Initialization), CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-54777?

4 open source packages ship an affected version, including CoreWCF.NetNamedPipe.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `CoreWCF.NetNamedPipe` | NuGet | All versions | 1.8.1 |
| `CoreWCF.NetNamedPipe` | NuGet | All versions | 1.8.1 |
| `CoreWCF.NetNamedPipe` | NuGet | From 1.9.0 | 1.9.1 |
| `CoreWCF.NetNamedPipe` | NuGet | From 1.9.0 | 1.9.1 |

## How do I fix CVE-2026-54777?

Upgrade CoreWCF.NetNamedPipe to a fixed version for your release line: 1.8.1 or 1.9.1.

## Is CVE-2026-54777 being exploited?

There is no known exploitation of CVE-2026-54777 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-54777 and fix it if it is affected.

What it is: CVE-2026-54777 is a medium-severity vulnerability in CoreWCF, published on 8 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-2026-54777 in the wild and no public exploit code.

Affected packages and fixed versions:
- CoreWCF.NetNamedPipe (NuGet): affected all versions; fixed in 1.8.1
- CoreWCF.NetNamedPipe (NuGet): affected all versions; fixed in 1.8.1
- CoreWCF.NetNamedPipe (NuGet): affected from 1.9.0; fixed in 1.9.1
- CoreWCF.NetNamedPipe (NuGet): affected from 1.9.0; fixed in 1.9.1

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-2026-54777/ (Markdown: https://insights.sbomify.com/CVE-2026-54777/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-54777
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-54777
- OSV: https://osv.dev/vulnerability/CVE-2026-54777

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-54777/
Summaries are generated and may contain mistakes; the official description above is the record.