CVE-2026-55428

HIGHPre-NVD 8.28.2
EchelonGraph scoreLOW confidence

This high-severity CVE scores 8.2 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: cna:github_m
8.2
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: —CVSS: 8.2Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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

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!

CVSS v3
8.2
EG Score
8.2(low)
EPSS
—
KEV
Not listed

Published

July 6, 2026

Last Modified

July 6, 2026

Vendor Advisories for CVE-2026-55428(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Data Freshness Timeline

(refreshed 1× in last 7d / 1× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-06 21:35 UTCEG score recompute

Frequently asked(4)

What is CVE-2026-55428?
CVE-2026-55428 is a high vulnerability published on July 6, 2026. Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator 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…
When was CVE-2026-55428 disclosed?
CVE-2026-55428 was first published in the National Vulnerability Database on July 6, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
What is the CVSS score of CVE-2026-55428?
CVE-2026-55428 has a CVSS v4.0 base score of 8.2 (CNA self-assessment; NVD's own analysis pending). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-55428?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55428, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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