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Advisory record · GHSA-q382-vc8q-7jhj

Improper handling of null Unicode character when parsing JSON in github.com/modelcontextprotocol/go-sdk

CVSS 4.0, no score published

Published by the GitHub Advisory Database at 19 Mar 2026, 12:44 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
github.com/modelcontextprotocol/go-sdkGo<1.4.11.4.1
Identifiers
GHSA-q382-vc8q-7jhj · GO-2026-4770
Weakness (CWE)
CWE-436 · CWE-1395
Tags
Published
19 Mar 2026
Updated
10 Sept 2026

Machine-written summary

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

The Go SDK github.com/modelcontextprotocol/go-sdk versions before 1.4.1 are affected. Its JSON parsing treated keys with null Unicode characters appended to them as equal to the base key, so when duplicate keys were present the last one could override the intended message. An attacker able to send crafted MCP messages could potentially evade proxies or policy layers that match exact field names. Upgrade to version 1.4.1 or later.

Written 1 Nov 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
Not published None 4.0 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:L/SA:N GitHub Advisory Database
  • CISA KEV Not listed.
  • EPSS No score.

Timeline

  1. 31 Oct 2026, 14:14 UTC First seen by agentprime
  2. 31 Oct 2026, 14:14 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.