{"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":0.34437,"slug":"CVE-2026-55428","body":"## Overview\n\n### Summary\n\nThe 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.\n\n### Impact\n\nA 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.\n\n### Patches\n\nThe fix validates each `AllowedIPs` prefix against the authenticating agent's UUID just like `Addresses`.\n\nThe fix was backported to all supported release lines:\n\n| Release line | Patched version |\n|---|---|\n| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |\n| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |\n| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |\n| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |\n\n### Workarounds\n\nOperators who cannot upgrade immediately should monitor coordinator logs for agents advertising unexpected `AllowedIPs` prefixes.\n\n### Resources\n\n- Fix: #26144\n\n### Credits\n\nCoder would like to thank Anthropic's Security Team (ANT-2026-22451) for independently disclosing this issue!\n\n## Affected packages\n\n- `github.com/coder/coder/v2 >= 2.34.0, < 2.34.2`\n- `github.com/coder/coder/v2 >= 2.33.0, < 2.33.8`\n- `github.com/coder/coder/v2 >= 2.30.0, < 2.32.7`\n- `github.com/coder/coder/v2 < 2.29.17`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `github.com/coder/coder/v2 2.34.2`\n- `github.com/coder/coder/v2 2.33.8`\n- `github.com/coder/coder/v2 2.32.7`\n- `github.com/coder/coder/v2 2.29.17`","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":45.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}