CVE-2026-77272

MEDIUM 5.4

MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler

CVSS Score

5.4

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-79
Vendor	sooperset
Product	mcp-atlassian
Published	Sep 22, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

Low

Integrity

Low

Availability

None

Affected Versions

sooperset / mcp-atlassian

< 0.22.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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