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Advisory record · GHSA-g2r2-3j32-j27x

MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler

CVSS 5.4 MediumEPSS 0.0026 · 18th percentile

Published by the GitHub Advisory Database at 22 Sept 2026, 20:35 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
mcp-atlassianPyPI<0.22.00.22.0
Identifiers
GHSA-g2r2-3j32-j27x · CVE-2026-77272 · PYSEC-2026-4093
Weakness (CWE)
CWE-79
Tags
Published
22 Sept 2026
Updated
1 Oct 2026

Machine-written summary

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

The mcp-atlassian package, versions before 0.22.0, has a reflected cross-site scripting flaw in the OAuth setup wizard's local callback server, which echoes the error query parameter into its HTML response without escaping. An attacker can get a victim to open a crafted callback link while the setup wizard is running, executing script in the victim's browser; the server also binds to all network interfaces, so the attack can come from the local network. Upgrade to mcp-atlassian 0.22.0 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
5.4 Medium 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0026, the 18th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:09 UTC First seen by agentprime
  2. 31 Oct 2026, 14:09 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.