2026-08-17-deepseek-harness-nothing-authenticates-the-web-ui-on-127-0-0-1-3080-and-the-api-fence

Nothing authenticates the Web UI on 127.0.0.1:3080, and the /api fence says so in its own header comment.

The answer to "what authenticates a request to the Web UI" is: nothing, and DeepSeek documents that rather than implying otherwise. packages/client/connection/src/api-request-trust.ts opens with "Network reachability and authentication stay out of scope: binding policy belongs to the webserver config, and this fence is not an auth layer." What isTrustedApiRequest() does is check the Host header against loopback or a declared trustedHosts authority, refuse an explicit sec-fetch-site: cross-site, and require any attached Origin to match the Host -- a DNS-rebinding and cross-site fence, not an identity check; an absent Origin passes. docs/subsystems/web-server.md is equally plain about the carrier: "there is no TLS, auth, or origin policy, so a non-loopback bind exposes the server to that network." The consequence is that any local process, any other user on a shared machine, and anything that can run curl against 127.0.0.1:3080 has the full API -- sessions, agents, and the bash tool behind them.

Channel: preview-or-beta. Ancestry: Both files read at tag commit 99f6f02fecdb7dff40c3fbc9470f5907c29f74ca, which git ls-remote --tags shows is the sole tag and which the release API flags prerelease: true. The fence's last change, 0a42836fbb (2026-08-13), compares behind / ahead_by 0 against that tag.

Operator consequence: Re-audit, and treat port 3080 as a shell. On a multi-user or shared-tenant host, dsh web hands every local account the agent's command execution. Do not add --trusted-host to make a LAN bind work -- that flag exists to satisfy the rebinding fence, and satisfying the fence is not authenticating anyone. Until an auth layer lands, the only defensible deployment is a single-user machine on loopback, reached remotely by SSH tunnel.

Receipt

• https://github.com/deepseek-ai/deepseek-harness/blob/99f6f02fecdb7dff40c3fbc9470f5907c29f74ca/packages/client/connection/src/api-request-trust.ts