What is the CVSS score of CVE-2026-55428?

CVE-2026-55428 has a CVSS 3.1 base score of 8.2 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N. EPSS exploitation probability: 0.4%.

Which versions of Coder are affected by CVE-2026-55428?

Coder's tailnet coordinator contains an authorization bypass vulnerability (CVE-2026-55428, CVSS 8.2) permitting interception of encrypted terminal sessions and workspace application traffic across…. A patch is available.

How to fix or mitigate CVE-2026-55428?

Within 24 hours: Identify all Coder deployments and document current versions. Within 7 days: Patch available per vendor advisory-obtain and test in staging environment. Within 30 days: Deploy patch to all production Coder instances.

Coder CVE-2026-55428

HIGH

Improper Authorization (CWE-285)

2026-07-06 https://github.com/coder/coder

GHSA-wrq8-fcv5-8hvp

Authentication Bypass

8.2

CVSS 3.1 · Vendor: https://github.com/coder/coder

Severity by source

Vendor (https://github.com/coder/coder) PRIMARY

8.2 HIGH

AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N

vuln.today AI

8.2 HIGH

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.

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

4.0 AV:N/AC:H/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N

Primary rating from Vendor (https://github.com/coder/coder).

CVSS VectorVendor: https://github.com/coder/coder

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 06, 2026 - 21:53 vuln.today

DescriptionCVE.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:

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 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. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Authenticate and provision workspace

Delivery

Deploy modified agent binary

Exploit

Advertise victim's tailnet prefix as AllowedIPs

Execution

Coordinator forwards prefix to peers

Persist

Traffic rerouted to attacker

Impact

Intercept and serve spoofed content

Access

Authenticate and provision workspace

Delivery

Deploy modified agent binary

Exploit

Advertise victim's tailnet prefix as AllowedIPs

Execution

Coordinator forwards prefix to peers

Persist

Traffic rerouted to attacker

Impact

Intercept and serve spoofed content

Vulnerability AssessmentAI

Exploitation	Exploitation requires an authenticated Coder user (PR:L) who owns a running workspace and replaces the standard workspace agent with a modified binary that advertises attacker-chosen WireGuard AllowedIPs prefixes overlapping a victim agent's tailnet address. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	The signals paint a credible but conditional threat. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	An authenticated user on a shared Coder deployment provisions a workspace and replaces its agent with a modified binary that advertises AllowedIPs containing a colleague's workspace tailnet prefix. The coordinator forwards the forged prefix to tunnel peers, causing web terminal and workspace app traffic destined for the victim to be routed to the attacker, who serves spoofed content or captures the session. …
Remediation	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. … Detailed patch versions, workarounds, and compensating controls in full report.