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.
- 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
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.
Which versions are affected by CVE-2026-77339?
3 open source packages ship an affected version, including github.com/f1bonacc1/process-compose.
| Package | 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.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-77339 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77339 exists.
Sources
Also known as GHSA-5gm3-9crp-6g3v, GO-2026-6515.