Coder CVE-2026-55428
HIGH
GHSA-wrq8-fcv5-8hvp
Severity by source
AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N
PR:L for an authenticated workspace owner and AC:H for needing a modified agent that correctly claims the victim's prefix; S:C as another agent's traffic is compromised, C:H/I:H from interception and spoofing, A:N.
Primary rating from Vendor (https://github.com/coder/coder).
CVSS VectorVendor: https://github.com/coder/coder
Lifecycle Timeline
1DescriptionCVE.org
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:
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!
AnalysisAI
Traffic interception in Coder's tailnet coordinator allows a malicious workspace agent to hijack another agent's tailnet address by advertising forged WireGuard AllowedIPs prefixes. The coordinator authorizes an agent's Addresses against its authenticated UUID but performs no equivalent check on AllowedIPs, which it forwards verbatim to tunnel peers; because ServerTailnet routes by tailnet IP, an attacker who claims a victim's prefix can intercept web terminal and workspace app traffic and serve spoofed content. Rated CVSS 8.2 (CWE-285, improper authorization); a vendor patch is available and no public exploit is identified at time of analysis.
Technical ContextAI
Coder builds encrypted overlay connectivity between the control plane and workspace agents using a Tailscale-derived tailnet stack over WireGuard. Each agent registers with a coordinator that distributes peer node information; the coordinator installs each peer's AllowedIPs into the WireGuard configuration, which determines which destination IP prefixes are routed to that peer. The root cause is CWE-285 (Improper Authorization): the coordinator correctly derives and validates that an agent's Addresses correspond to its authenticated UUID but omits the same ownership check for AllowedIPs. Because Coder's ServerTailnet routes to agents strictly by tailnet IP, an unchecked AllowedIPs advertisement lets one authenticated peer install routing entries that steer another agent's address prefix to itself. CPE data identifies the affected component as the Go module pkg:go/github.com/coder/coder/v2 (the coder/coder server).
RemediationAI
Vendor-released patch: upgrade to the fixed release for your line - v2.34.2, v2.33.8, v2.32.7, or v2.29.17 (ESR) - which adds validation of each AllowedIPs prefix against the authenticating agent's UUID, matching the existing Addresses check. See the advisory at https://github.com/coder/coder/security/advisories/GHSA-wrq8-fcv5-8hvp and fix PR https://github.com/coder/coder/pull/26144. Operators who cannot upgrade immediately should monitor coordinator logs for agents advertising unexpected or overlapping AllowedIPs prefixes (the vendor-recommended workaround); note this is detective only and does not prevent interception, so also consider limiting workspace creation to trusted users and reviewing multi-tenant exposure until patched.
Same weakness CWE-285 – Improper Authorization
View allSame technique Authentication Bypass
View allVendor StatusVendor
SUSE
Severity: Important| Product | Status |
|---|---|
| SUSE Linux Enterprise Server 16.1 | Affected |
| SUSE Linux Enterprise Server for SAP applications 16.1 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP5 | Affected |
| SUSE Linux Enterprise Module for Package Hub 15 SP6 | Affected |
| openSUSE Leap 15.5 | Affected |
| openSUSE Leap 15.6 | Affected |
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External POC / Exploit Code
Leaving vuln.today