Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.2 · CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

EPSS

• CVE-2026-55428: 0.40% estimated exploitation activity in the next 30 days; percentile 34.78 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

6 Jul 2026, 20:58 UTC

Last modified by the source

6 Jul 2026, 20:58 UTC

Source last checked

26 Oct 2026, 15:24 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wrq8-fcv5-8hvp

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# Patch Next advisory brief: CVE-2026-55428

Advisory: Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator
IDs: CVE-2026-55428, GHSA-wrq8-fcv5-8hvp
Record: https://patchnext.com/advisories/cve-2026-55428 (revision 1, source checked 26 Oct 2026, 15:24 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/coder/coder/v2 2.34.2, 2.33.8, 2.32.7, 2.29.17. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/coder/coder/v2: affected >= 2.34.0, < 2.34.2; >= 2.33.0, < 2.33.8; >= 2.30.0, < 2.32.7; < 2.29.17; fixed in 2.33.8, 2.29.17, 2.34.2, 2.32.7

## Suggested inspection (read-only)
- Go github.com/coder/coder/v2: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/coder/coder/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-wrq8-fcv5-8hvp (GitHub-reviewed advisory GHSA-wrq8-fcv5-8hvp lists affected ranges: Go github.com/coder/coder/v2 >=2.34.0 =2.33.0 =2.30.0 =0 <2.29.17)

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