Sliver One-Click Remote Access: Insecure CORS & Unauthenticated MCP Interface

Exploitation

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

CVSS 4.0

5.9 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-34227: 0.41% estimated exploitation activity in the next 30 days; percentile 35.41 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

A single click on a malicious link gives an unauthenticated attacker immediate, silent control over every active C2 session or beacon, capable of exfiltrating all collected target data (e.g. SSH keys, ntds.dit) or destroying the entire compromised infrastructure, entirely through the operator's own browser. Description The Sliver MCP server runs inside the Sliver Client and binds an unauthenticated HTTP and SSE interface to localhost:8080 by default. The service returns a permissive Access-Control-Allow-Origin: header on all responses. Because this server is client-side, the attack surface is distributed across every individual operator in the operation. Any arbitrary website can issue cross-origin requests and interact with the MCP interface via an operator's browser, no credentials required. If the interface is misconfigured to bind to all interfaces (0.0.0.0), the vulnerability escalates from a client-side CSRF/CORS issue to direct, unauthenticated remote access from any actor on…

Published by the source

31 Mar 2026, 23:07 UTC

Last modified by the source

31 Mar 2026, 23:07 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6fpf-248c-m7wm

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# Patch Next advisory brief: CVE-2026-34227

Advisory: Sliver One-Click Remote Access: Insecure CORS & Unauthenticated MCP Interface
IDs: CVE-2026-34227, GHSA-6fpf-248c-m7wm
Record: https://patchnext.com/advisories/cve-2026-34227 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/bishopfox/sliver 1.7.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/bishopfox/sliver: affected <= 1.7.3; fixed in 1.7.4

## Suggested inspection (read-only)
- Go github.com/bishopfox/sliver: 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 github.com/bishopfox/sliver.
- 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-6fpf-248c-m7wm (GitHub-reviewed advisory GHSA-6fpf-248c-m7wm lists affected ranges: Go github.com/bishopfox/sliver >=0 <=1.7.3)

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