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Vulnerability · Published Aug 25, 2026 · Assigned by GitHub_M

CVE-2026-55637genieacs-mcp: DNS rebinding reaches local GenieACS MCP Streamable HTTP transport

High 8.8

In plain English

A high-severity security flaw in genieacs-mcp from GeiserX. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)8.8High
Exploit odds (30 days)0.3%top 81.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

genieacs-mcp is an MCP server for GenieACS written in Go. Prior to 0.3.2, the Streamable HTTP transport in cmd/server/main.go creates an unauthenticated /mcp listener on the default MCP_LISTEN_ADDR value 127.0.0.1:8080 when MCP_AUTH_TOKEN is unset and the httpSrv.Start(addr) branch does not validate the Host or Origin headers. A malicious website can use DNS rebinding to send browser requests with attacker-controlled Host and Origin values to the loopback listener, initialize an MCP session, list tools, and invoke operations against the GenieACS NBI configured by ACS_URL. Successful exploitation can expose or modify CPE management state, including device reboots, firmware tasks, TR-069 parameter changes, presets, provisions, tags, connection requests, and task operations. The npm wrapper is not affected because it forces TRANSPORT=stdio and does not expose an HTTP listener. This issue is fixed in version 0.3.2.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/geiserx/genieacs-mcp0.3.2GHSA-cmwv-wf9p-p8wx
Gogithub.com/geiserx/genieacs-mcp0.3.2GO-2026-6295

Affected products (as reported)

VendorProductVersions
GeiserX genieacs-mcp < 0.3.2

Weakness: CWE-346 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N

References