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CVE-2026-77272 medium CVSS 5.4

Cross-Site Scripting (XSS) in mcp-atlassian (CVE-2026-77272)

Summary

Cross-site scripting in mcp-atlassian (CVE-2026-77272). Risk of unauthorized operations or information disclosure. Exploitable via error. Mitigation: upgrade to 0.22.0 or later.

Original description

The description as published by the source.

Summary

The OAuth 2.0 setup wizard's local callback HTTP server reflects the error query parameter directly into an HTML response without any sanitization or encoding. An attacker can craft a malicious callback URL containing JavaScript in the error parameter that executes in the victim's browser when the setup wizard is running. The server binds to all network interfaces (0.0.0.0), making it accessible from the local network rather than just localhost.

Details

The vulnerability exists in the CallbackHandler class in src/mcp_atlassian/utils/oauth_setup.py.

Step 1 -- Attacker-controlled input enters unsanitized:

At line 63-66, the error query parameter from the URL is read and interpolated into a message string without HTML escaping:

# src/mcp_atlassian/utils/oauth_setup.py:63-66
if "error" in params:
    callback_error = params["error"][0]
    callback_received = True
    self._send_response(f"Authorization failed: {callback_error}")

Step 2 -- Unsanitized input is injected into HTML:

At line 124-125 in _send_response, the message variable (containing the unescaped attacker input) is injected directly into the HTML template via f-string interpolation:

# src/mcp_atlassian/utils/oauth_setup.py:124-125

    {message}

Step 3 -- Server listens on all interfaces:

At line 167, the callback server binds to all network interfaces, not just localhost:

# src/mcp_atlassian/utils/oauth_setup.py:167
httpd =…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-77272 has been found in mcp-atlassian.
Attackers can target a specific entry point like error over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade mcp-atlassian to 0.22.0 or later.
If unsure, ask your IT team or search "mcp-atlassian CVE-2026-77272" on the vendor's site.

CVE-2026-77272 (mcp-atlassian) — CWE-79 / CVSS v3 5.4
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: error / CallbackHandler / _send_response / message
Patched: 0.22.0 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Cross-site scripting (XSS) (CWE-79) exists in mcp-atlassian. Attackers reach the vulnerable code path via error without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of mcp-atlassian. Attack surface: error / CallbackHandler / _send_response / message.

🔥 Severity

Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 0.22.0.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'mcp-atlassian' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'mcp-atlassian' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で mcp-atlassian を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade mcp-atlassian to 0.22.0

    ステージング環境で 0.22.0 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

pip mcp-atlassian
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.22.0"}]}]
PyPI mcp-atlassian
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.22.0"}]}]

References

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