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Vulnerability · Published Sep 22, 2026 · Assigned by GitHub_M

CVE-2026-77272MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler

Medium 5.4

In plain English

A medium-severity cross-site scripting in mcp-atlassian from sooperset. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 18% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.4Medium
Exploit odds (30 days)0.3%top 81.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

MCP Atlassian is a Model Context Protocol (MCP) server for Atlassian products (Confluence and Jira). Prior to 0.22.0, the OAuth error query parameter is passed to CallbackHandler._send_response in oauth_setup.py and interpolated into an HTML page without escaping. A crafted authorization callback can inject markup or script that executes in the browser of a user completing the OAuth flow. This issue is fixed in version 0.22.0.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
PyPImcp-atlassian0.22.0GHSA-g2r2-3j32-j27x
PyPImcp-atlassian0.22.0PYSEC-2026-4093

Affected products (as reported)

VendorProductVersions
sooperset mcp-atlassian < 0.22.0

Weakness: CWE-79 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

References