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Advisory record · GHSA-4mfg-r38w-w8fg

mcp-sanitizer: URL sanitizer allows localhost/IPv6 loopback SSRF bypass via explicit port or bracketed IPv6

CVSS 8.2 High

Published by the GitHub Advisory Database at 28 Oct 2026, 19:51 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
mcp-sanitizernpm<1.4.01.4.0
Identifiers
GHSA-4mfg-r38w-w8fg
Weakness (CWE)
CWE-918
Tags
Published
28 Oct 2026
Updated
28 Oct 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

The mcp-sanitizer npm package, versions before 1.4.0, has a URL validation gap in which localhost URLs with an explicit port and bracketed IPv6 loopback or link-local addresses are not blocked, allowing server-side request forgery. An unauthenticated attacker who can supply the URL parameter of a web_fetch or web_scraper tool can get the sanitizer to approve internal targets, potentially reading responses from internal services. The fix is to upgrade to version 1.4.0.

Written 31 Oct 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
8.2 High 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N GitHub Advisory Database
  • CISA KEV Not listed.
  • EPSS No score.

Timeline

  1. 31 Oct 2026, 13:33 UTC First seen by agentprime
  2. 31 Oct 2026, 13:33 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.