# CVE-2026-77339: Process Compose: Browser DNS rebinding lets websites control local process-compose MCP tools

> A malicious website can use DNS rebinding to control local processes and access logs if MCP SSE and control tools are enabled.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:L/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 18 Sep 2026
- **Updated:** 18 Sep 2026
- **Also known as:** GHSA-5gm3-9crp-6g3v, GO-2026-6515

## What is CVE-2026-77339?

CVE-2026-77339 is a medium-severity server-side request forgery vulnerability in F1bonacc1 process-compose, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Process Compose is a scheduler and orchestrator for non-containerized applications. Prior to 1.120.0, the MCP SSE listener in src/mcp/server.go accepts browser-origin requests to /sse and the returned message endpoint without validating the Host header, validating the Origin header, or authenticating the caller. When MCP SSE is enabled, a malicious website can use DNS rebinding to reach the loopback listener and issue MCP requests. If expose_control_tools is enabled, the attacker can enumerate process state, read or search logs, truncate logs, and start, stop, restart, or scale local processes; configured user-defined tools can expose additional commands and output. The Gin REST API token middleware does not protect this separately started MCP listener. This issue is fixed in version 1.120.0.

Weakness: CWE-346 (Origin Validation Error), CWE-306 (Missing Authentication for Critical Functionality)

## Which versions are affected by CVE-2026-77339?

3 open source packages ship an affected version, including github.com/f1bonacc1/process-compose.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/f1bonacc1/process-compose` | Go | All versions | 1.120.0 |
| `github.com/f1bonacc1/process-compose` | Go | All versions | 1.120.0 |
| `github.com/f1bonacc1/process-compose` | Go | All versions | 1.120.0 |

## How do I fix CVE-2026-77339?

Upgrade github.com/f1bonacc1/process-compose to 1.120.0 or later.

## Is CVE-2026-77339 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77339 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77339 and fix it if it is affected.

What it is: CVE-2026-77339 is a medium-severity server-side request forgery vulnerability in F1bonacc1 process-compose, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77339 exists.

Affected packages and fixed versions:
- github.com/f1bonacc1/process-compose (Go): affected all versions; fixed in 1.120.0
- github.com/f1bonacc1/process-compose (Go): affected all versions; fixed in 1.120.0
- github.com/f1bonacc1/process-compose (Go): affected all versions; fixed in 1.120.0

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-2026-77339/ (Markdown: https://insights.sbomify.com/CVE-2026-77339/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77339
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77339
- OSV: https://osv.dev/vulnerability/CVE-2026-77339

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77339/
Summaries are generated and may contain mistakes; the official description above is the record.