CVE-2026-77272
Received Received - Intake

Stored XSS in MCP Atlassian OAuth Flow

Publication date: 2026-09-22

Last updated on: 2026-09-22

Assigner: GitHub, Inc.

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.

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Meta Information

Published
2026-09-22
Last Modified
2026-09-22
Generated
2026-09-22
AI Q&A
2026-09-22
EPSS Evaluated
N/A
NVD
CVE-2026-77272
EUVD
EUVD-2026-84749

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
atlassian mcp to 0.22.0 (exc)
atlassian mcp 0.22.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-79 The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

Attack-Flow Graph

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Executive Summary

CVE-2026-77272 is a reflected Cross-Site Scripting (XSS) vulnerability in the mcp-atlassian package affecting versions prior to 0.22.0. It occurs in the OAuth 2.0 setup process where the error query parameter is reflected into an HTML response without proper sanitization. An attacker can craft a malicious callback URL with JavaScript in the error parameter, which executes in the victim's browser during the OAuth setup flow.

Detection Guidance

Check if the mcp-atlassian package version is below 0.22.0 by running: pip show mcp-atlassian. If installed, verify if the OAuth setup callback server is running on 0.0.0.0 instead of localhost by checking network bindings with netstat -tulnp | grep python.

Impact Analysis

This vulnerability allows an attacker to execute JavaScript in the victim's browser during the OAuth setup process. This could lead to interception or manipulation of the OAuth authorization code, potentially compromising user sessions or sensitive data processed during the setup.

Mitigation Strategies

Upgrade the mcp-atlassian package to version 0.22.0 or later using pip install --upgrade mcp-atlassian. Ensure the OAuth callback server is bound to localhost only by modifying the server configuration to restrict network access.

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