CVE-2026-77272: mcp atlassian XSS — Exploit & Fix

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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CVSS v3.1 Score

5.4

MEDIUM

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

EPSS — Exploit Prediction

0.0025

Probability of exploitation

0.15%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

Affected Products

Vendor	Product	Versions
mcp-atlassian	mcp_atlassian	< 0.22.0

References

Advisories & Patches

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

Exploits

https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g2r2-3j32-j27x

Other References

https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0

Frequently Asked Questions

What is CVE-2026-77272? +

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. It has a CVSS v3.1 base score of 5.4 (MEDIUM).

How severe is CVE-2026-77272? +

CVE-2026-77272 has a CVSS v3.1 score of 5.4 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0025, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-77272? +

CVE-2026-77272 affects products from mcp-atlassian, specifically: mcp_atlassian. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-77272? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-77272