GHSA-wrq8-fcv5-8hvp: Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator

Summary The tailnet coordinator validates that an agent's Addresses derive from its authenticated UUID but applies no equivalent check to AllowedIPs. The coordinator forwards agent-supplied AllowedIPs verbatim to tunnel peers which install them into the WireGuard peer configuration. Impact A malicious workspace agent can advertise arbitrary AllowedIPs prefixes including another agent's tailnet address. Coder's ServerTailnet routes to agents by tailnet IP so an agent that claims a victim's prefix can intercept web terminal and workspace app traffic and serve spoofed content. Exploitation requires an authenticated user with a running workspace and a modified agent binary. Patches The fix validates each AllowedIPs prefix against the authenticating agent's UUID just like Addresses. The fix was backported to all supported release lines: | Release line | Patched version | |---|---| | 2.34 | v2.34.2 | | 2.33 | v2.33.8 | | 2.32 | v2.32.7 | | 2.29 (ESR) | v2.29.17 | Workarounds Operators who cannot upgrade immediately should monitor coordinator logs for agents advertising unexpected AllowedIPs prefixes. Resources - Fix: #26144 Credits Coder would like to thank Anthropic's Security Team (ANT-2026-22451) for independently disclosing this issue!