# CVE-2026-77272: MCP Atlassian: Reflected XSS in OAuth Setup Callback Handler

> Attackers can inject scripts into the OAuth callback page, executing code in the victim's browser during the authentication flow.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 22 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** GHSA-g2r2-3j32-j27x, PYSEC-2026-4093

## What is CVE-2026-77272?

CVE-2026-77272 is a medium-severity cross-site scripting vulnerability in sooperset mcp-atlassian, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-77272?

3 open source packages ship an affected version, including mcp-atlassian. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mcp-atlassian` | PyPI | All versions | 0.22.0 |
| `mcp-atlassian` | PyPI | All versions | 0.22.0 |
| `mcp-atlassian` | PyPI | All versions | 0.22.0 |

Products: Mcp-Atlassian Mcp Atlassian.

## How do I fix CVE-2026-77272?

Upgrade mcp-atlassian to 0.22.0 or later.

## Is CVE-2026-77272 being exploited?

There is no known exploitation of CVE-2026-77272 in the wild and no public exploit code.

## Other vulnerabilities in sooperset mcp-atlassian

- [CVE-2026-77244](https://insights.sbomify.com/CVE-2026-77244/): [mcp-atlassian] Authentication bypass in HTTP transport: AtlassianOpaqueTokenVerifier accepts any non-empty token (critical 10.0)
- [CVE-2026-77254](https://insights.sbomify.com/CVE-2026-77254/): MCP Atlassian: Unauthenticated HTTP MCP requests can use globally configured Jira and Confluence credentials (critical 9.1)
- [CVE-2026-27825](https://insights.sbomify.com/CVE-2026-27825/): MCP Atlassian has an arbitrary file write leading to arbitrary code execution via unconstrained download_path in confluence_download_attachment (critical 9.1)
- [CVE-2026-77243](https://insights.sbomify.com/CVE-2026-77243/): MCP Atlassian: ENABLED_TOOLS / Toolset authorization bypass (high 8.8)
- [CVE-2026-77274](https://insights.sbomify.com/CVE-2026-77274/): MCP Atlassian: SSRF Protection Bypass (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77272 and fix it if it is affected.

What it is: CVE-2026-77272 is a medium-severity cross-site scripting vulnerability in sooperset mcp-atlassian, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-77272 in the wild and no public exploit code.

Affected packages and fixed versions:
- mcp-atlassian (PyPI): affected all versions; fixed in 0.22.0
- mcp-atlassian (PyPI): affected all versions; fixed in 0.22.0
- mcp-atlassian (PyPI): affected all versions; fixed in 0.22.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-77272/ (Markdown: https://insights.sbomify.com/CVE-2026-77272/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77272
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77272
- OSV: https://osv.dev/vulnerability/CVE-2026-77272

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77272/
Summaries are generated and may contain mistakes; the official description above is the record.