What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-09-22 · updated 2026-09-28
• Weakness: CWE-79

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 products

• sooperset mcp-atlassian: before 0.22.0 — fixed in 0.22.0

How to fix

Upgrade to a fixed version: sooperset mcp-atlassian 0.22.0. Check the vendor advisory for mitigations.

References

• https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
• https://github.com/sooperset/mcp-atlassian/pull/1448
• https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
• https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g2r2-3j32-j27x

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