VULNpocalypse

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

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.

What it is

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.

Description quoted from the CVE record (assigned by GitHub_M, published 2026-09-18).

Weakness: CWE-306: Missing Authentication for Critical Function; CWE-346: Origin Validation Error

How it can be exploited

Exploitable over the network with low attack complexity only when specific conditions are present needing no privileges and a user must take an action. Impact: confidentiality low, integrity low, availability none. 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

CISA assessment (SSVC): CISA assesses that a public proof of concept exists. Automatable: no. Technical impact: partial.

Public exploit evidence (Exploit Observer)

Also known as: EUVD-2026-83168, GHSA-5gm3-9crp-6g3v

VEDAS cluster: VEDAS:DEWDROPHEDGEHOG

Exploit Observer links 2 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (2)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Vulnerability databases and vendor advisories (5)

Catalogue entries, not exploit evidence.

3 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS
0.003
low predicted chance of attack
VEDAS
0.987
strong exploit evidence
On CISA KEV
Not listed
Detection rule
Nuclei

Who is affected

ProductAffectedNot affected
F1bonacc1 process-composeversion < 1.120.0Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

Exploit Observer also maps it to: go github.com/f1bonacc1/process-compose.

How to fix it

No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.

How to detect it

Nuclei template (active check)

Process Compose - MCP SSE Listener Missing Origin/Host Validation

Process Compose prior to 1.120.0 exposes its MCP Server-Sent Events listener at GET /sse without validating the Host or Origin header and without authenticating the caller. The separately started MCP listener is not protected by the Gin REST API token middleware, so a cross-origin browser request receives the SSE endpoint event and an Access-Control-Allow-Origin wildcard, enabling DNS-rebinding attacks that can enumerate and control local processes. This template sends an unauthenticated cross-origin GET to /sse and confirms the listener returns the SSE event stream with a wildcard CORS header, proving the missing origin/authentication controls.

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (GET /sse); it decides using status, word matchers. Severity in the template: high. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash
nuclei -u https://your-host -t CVE-2026-77339.yaml
Show the template (48 lines)
yaml
id: CVE-2026-77339

info:
  name: "Process Compose - MCP SSE Listener Missing Origin/Host Validation"
  author: vedas-arpsyndicate
  severity: high
  description: |
    Process Compose prior to 1.120.0 exposes its MCP Server-Sent Events listener at GET /sse
    without validating the Host or Origin header and without authenticating the caller. The
    separately started MCP listener is not protected by the Gin REST API token middleware, so a
    cross-origin browser request receives the SSE endpoint event and an Access-Control-Allow-Origin
    wildcard, enabling DNS-rebinding attacks that can enumerate and control local processes. This
    template sends an unauthenticated cross-origin GET to /sse and confirms the listener returns the
    SSE event stream with a wildcard CORS header, proving the missing origin/authentication controls.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2026-77339&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=process-compose&match=exact
  classification:
    cve-id: CVE-2026-77339
    cwe-id: CWE-346
  metadata:
    verified: false
    max-request: 1
  tags: cve,cve2026,process-compose,mcp,sse,dns-rebinding,auth-bypass

http:
  - raw:
      - |
        GET /sse HTTP/1.1
        Host: {{Hostname}}
        Accept: text/event-stream
        Origin: https://evil.example

    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        part: header
        words:
          - "text/event-stream"
          - "Access-Control-Allow-Origin: *"
        condition: and
      - type: word
        part: body
        words:
          - "sessionId="

CVE-2026-77339.yaml on GitHub

References

Other references

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.