---
id: CVE-2026-55428
aliases:
  - GHSA-wrq8-fcv5-8hvp
title: >-
  Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs
  in tailnet coordinator
summary: >-
  Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs
  in tailnet coordinator
severity: high
cvss: 8.2
cwe:
  - CWE-285
  - CWE-863
vendor: coder
product: github.com/coder/coder/v2
ecosystem: go
affected:
  - 'github.com/coder/coder/v2 >= 2.34.0, < 2.34.2'
  - 'github.com/coder/coder/v2 >= 2.33.0, < 2.33.8'
  - 'github.com/coder/coder/v2 >= 2.30.0, < 2.32.7'
  - github.com/coder/coder/v2 < 2.29.17
patched:
  - github.com/coder/coder/v2 2.34.2
  - github.com/coder/coder/v2 2.33.8
  - github.com/coder/coder/v2 2.32.7
  - github.com/coder/coder/v2 2.29.17
published: '2026-07-06'
updated: '2026-07-06'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-wrq8-fcv5-8hvp'
references:
  - url: 'https://github.com/coder/coder/security/advisories/GHSA-wrq8-fcv5-8hvp'
  - url: 'https://github.com/coder/coder/pull/26144'
  - url: 'https://github.com/advisories/GHSA-wrq8-fcv5-8hvp'
tags:
  - ghsa
  - go
ingestedAt: '2026-07-06T21:45:52.966Z'
epss: 0.00405
epssPercentile: 0.34542
---

## Overview

### 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!

## Affected packages

- `github.com/coder/coder/v2 >= 2.34.0, < 2.34.2`
- `github.com/coder/coder/v2 >= 2.33.0, < 2.33.8`
- `github.com/coder/coder/v2 >= 2.30.0, < 2.32.7`
- `github.com/coder/coder/v2 < 2.29.17`

## Remediation

Upgrade to a patched release:

- `github.com/coder/coder/v2 2.34.2`
- `github.com/coder/coder/v2 2.33.8`
- `github.com/coder/coder/v2 2.32.7`
- `github.com/coder/coder/v2 2.29.17`