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CVE-2026-55428 — Vulnerability in github.com/coder/coder/v2 — CVE...

HIGH

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

Published July 6, 2026Updated July 7, 2026Source: osv

Summary

### 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!

Advisory Timeline

  • First published July 6, 2026 (98 days ago).
  • Last revised July 7, 2026 — 1 day after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Go
Update github.com/coder/coder/v2 to 2.29.17 or later
go get github.com/coder/coder/v2@v2.29.17
Go
Update github.com/coder/coder/v2 to 2.34.2 or later
go get github.com/coder/coder/v2@v2.34.2
Go
Update github.com/coder/coder/v2 to 2.32.7 or later
go get github.com/coder/coder/v2@v2.32.7
Go
Update github.com/coder/coder/v2 to 2.33.8 or later
go get github.com/coder/coder/v2@v2.33.8

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (4)

Affects 1 ecosystem: go (1).

PackageEcosystemAffectedFixed In
github.com/coder/coder/v2
go
All versions2.29.17
github.com/coder/coder/v2
go
All versions2.34.2
github.com/coder/coder/v2
go
All versions2.32.7
github.com/coder/coder/v2
go
All versions2.33.8

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

  • CWE-285
    Improper AuthorizationMITRE
  • CWE-863
    Incorrect AuthorizationMITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 8.2 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
High
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

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

References

Frequently Asked Questions

What is CVE-2026-55428?
Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator This vulnerability has been assigned a severity rating of HIGH (CVSS score: 8.2/10).
How do I check if my project is affected by CVE-2026-55428?
CVE-2026-55428 affects github.com/coder/coder/v2. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-55428 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
8.2

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-wrq8-fcv5-8hvp
GO-2026-5915

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  • CVE-2026-107813
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  • CVE-2026-44454
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  • CVE-2026-55427
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  • CVE-2026-63443
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  • CVE-2026-55431
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