GHSA-wrq8-fcv5-8hvp
Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator
Details
### 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](https://github.com/coder/coder/releases/tag/v2.34.2) | | 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) | | 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) | | 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/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!
Are you affected?
Enter the version of the package you're using.
Affected packages
2.34.0 Fixed in: 2.34.2 go get github.com/coder/coder/v2@v2.34.2 2.33.0 Fixed in: 2.33.8 go get github.com/coder/coder/v2@v2.33.8 2.30.0 Fixed in: 2.32.7 go get github.com/coder/coder/v2@v2.32.7 0 Fixed in: 2.29.17 go get github.com/coder/coder/v2@v2.29.17