Medium severity · published Sep 22, 2026
CVE-2026-77272
MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler
6.1
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 18% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MC
mcp-atlassian · sooperset
< 0.22.0 · source: vendor
MA
Mcp Atlassian · Mcp-atlassian
before 0.22.0 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-77272
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-77272
Patch
https://github.com/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
Issue Tracking
https://github.com/sooperset/mcp-atlassian/pull/1448
Release Notes
https://github.com/sooperset/mcp-atlassian/releases/tag/v0.22.0
Exploit
https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g2r2-3j32-j27x
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