MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler (CVE-2026-77272) | HOL Guard CVE

Medium · CVSS 5.4CVE-2026-77272GHSA-G2R2-3J32-J27X

MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler

Answer in brief

CVE-2026-77272 records a Medium severity (CVSS 5.4) vulnerability in MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler. The current sources do not mark it as known exploited. The current feed maps sooperset/mcp-atlassian (generic), mcp-atlassian (pip). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 22, 2026Updated Sep 22, 2026Source checked Sep 22, 2026First seen by HOL Sep 22, 2026Material review Sep 22, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.4
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 5.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps sooperset/mcp-atlassian (generic), mcp-atlassian (pip). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
sooperset/mcp-atlassiangeneric	<0.22.0	0.22.0
mcp-atlassianpip	<0.22.0	0.22.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for sooperset/mcp-atlassian, mcp-atlassian.
Review the reported fix. Update sooperset/mcp-atlassian to 0.22.0; mcp-atlassian to 0.22.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 22, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 22, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.