CVE-2026-77272 json
MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler
published last mo. modified last mo. also EUVD-2026-84749 , GHSA-g2r2-3j32-j27x , PYSEC-2026-4093
- 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
- sooperset mcp_atlassian 0.22.0
- mcp-atlassian mcp_atlassian 0.22.0
Is CVE-2026-77272 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
- Assessed
- last mo.
Exploit prediction
0.26% chance of exploitation in the next 30 days, higher than 18% of all scored CVEs (FIRST EPSS, 2026-11-11).
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 |
| GitHub | 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 |
| 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
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.
CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.