CVE-2026-77272 json
MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler
published 2026-09-22 47 d ago modified 2026-10-01 38 d ago also GHSA-g2r2-3j32-j27x , PYSEC-2026-4093 , EUVD-2026-84749
- cvss
- 5.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 18%
- public exploits
- 0
- none known
Summary
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.
Patch / fix
- pypi mcp-atlassian 0.22.0
- mcp-atlassian mcp_atlassian 0.22.0
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- 47 d ago
Exploit prediction
0.26% chance of exploitation in the next 30 days, higher than 18% of all scored CVEs (FIRST EPSS, 2026-11-08).
Exploits and checks
- github.com https://github.com/sooperset/mcp-atlassian/security/advisories/GHSA-g2r2-3j32-j27x referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
| NVD | 3.1 | 6.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N |
| GitHub | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
| OSV | 3.1 | 5.4 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| pypi | mcp-atlassian | <0.22.0 |
0.22.0 |
Affected products
- sooperset mcp-atlassian
Classification
- Weakness
-
- CWE-79 Improper Neutralization of Input During Web Page Generation
References
-
github.com
/sooperset/mcp-atlassian/pull/1448
web, issue-tracking, patch
-
github.com
/sooperset/mcp-atlassian/commit/b041733473f95119dd539542a43c280737a8e460
web, patch
-
github.com
/sooperset/mcp-atlassian/security/advisories/GHSA-g2r2-3j32-j27x
web, exploit, vendor-advisory
-
github.com
/sooperset/mcp-atlassian/releases/tag/v0.22.0
web, release-notes
-
github.com
/sooperset/mcp-atlassian
package
-
pypi.org
/project/mcp-atlassian
package
-
github.com
/advisories/GHSA-g2r2-3j32-j27x
advisory
-
nvd.nist.gov
/vuln/detail/CVE-2026-77272
advisory
Sources
- CVE List CVE-2026-77272
- GitHub Advisory GHSA-g2r2-3j32-j27x
- NVD CVE-2026-77272
- OSV PYSEC-2026-4093
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