java-client Allows Network Pivot via Unvalidated directConnect Redirect in AppiumCommandExecutor

Summary

When directConnect(true) is enabled, appium/java-client unconditionally accepts directConnectHost, directConnectPort, and directConnectPath from the server's NEW_SESSION response and silently redirects all subsequent session traffic to the attacker-specified endpoint — with no allowlist, no host validation, and no user notification.

Affected Code

• AppiumCommandExecutor.java (line 196–219): setDirectConnect() builds a new URL from server-supplied fields and calls overrideServerUrl(newUrl) without validating host/IP.
• DirectConnect.java: getUrl() constructs protocol://host:port/path with no allowlist.

Root Cause

Only the protocol is validated (must equal "https"). The destination host and port are never checked against any allowlist or denylist.

PoC (confirmed)

A rogue server injecting directConnectHost=127.0.0.1:4443 causes the client to silently redirect all post-session commands:

[bootstrap] POST /wd/hub/session [bootstrap] Injecting directConnect -> https://127.0.0.1:4443/wd/hub [redirect-target] HIT #1: GET /wd/hub/session/poc-session-001/source [redirect-target] HIT #2: DELETE /wd/hub/session/poc-session-001

Original source code unmodified — confirmed via git diff HEAD (empty).

Evidence Screenshots

Screenshot 1 — Rogue server capturing redirected traffic:

<img width="887" height="146" alt="1" src="https://github.com/user-attachments/assets/cc28002c-ea20-4ac8-8336-cec632e3c842" />

Screenshot 2 — Java client processing response from attacker host:

<img width="788" height="130" alt="2" src="https://github.com/user-attachments/assets/222cbab0-0d53-45b2-847d-6aa4e3b79370" />

Impact

• Full interception of session traffic
• Network pivot to internal hosts (RFC-1918, 169.254.169.254)
• Cloud credential theft via IMDS endpoint
• Escalates to ~8.1 High in CI/CD environments where directConnect(true) is set in shared base configuration

Suggested Fix

Add allowlist validation before overrideServerUrl() is called, and/or block RFC-1918/loopback/link-local destinations by default.

poc_appium_directconnect.zip