goshs: SSH host key verification disabled, allowing transparent MITM of every tunnelled HTTP request

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.4 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Summary The --tunnel / -t flag opens an outbound SSH connection to localhost.run:22 with HostKeyCallback: ssh.InsecureIgnoreHostKey(). The Go documentation for that function states verbatim: "It should not be used for production code." With the callback disabled the client accepts any host key the server presents, so an attacker who can intercept the operator's TCP connection to localhost.run:22 (any router on the path, malicious local network, ARP/DNS spoof on the operator's LAN, BGP hijack, malicious VPN) can present their own SSH host key, terminate the SSH session locally, and proxy onward — sitting transparently in the middle of the tunnel. Because localhost.run does TLS termination at their end, the HTTP traffic on the SSH leg is plaintext, so the on-path attacker reads and rewrites every request and response in cleartext. The goshs operator gets no warning; the public URL works normally. Affected Code File: tunnel/tunnel.go There is no fallback verification — no…

Published by the source

15 May 2026, 17:17 UTC

Last modified by the source

15 May 2026, 17:17 UTC

Source last checked

26 Oct 2026, 15:22 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mxg3-432p-mr72

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# Patch Next advisory brief: GHSA-mxg3-432p-mr72

Advisory: goshs: SSH host key verification disabled, allowing transparent MITM of every tunnelled HTTP request
IDs: GHSA-mxg3-432p-mr72
Record: https://patchnext.com/advisories/ghsa-mxg3-432p-mr72 (revision 1, source checked 26 Oct 2026, 15:22 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: goshs.de/goshs/v2 2.0.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go goshs.de/goshs/v2: affected <= 2.0.6; fixed in 2.0.7

## Suggested inspection (read-only)
- Go goshs.de/goshs/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on goshs.de/goshs/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-mxg3-432p-mr72 (GitHub-reviewed advisory GHSA-mxg3-432p-mr72 lists affected ranges: Go goshs.de/goshs/v2 >=0 <=2.0.6)

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