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CVE-2026-55428 is a high-severity authorization flaw in Coder's tailnet coordinator. In affected versions, the coordinator verifies that an agent's Addresses are derived from the agent's authenticated UUID, but it does not perform equivalent validation for agent-supplied AllowedIPs. As a result, the coordinator forwards AllowedIPs values from the agent verbatim to tunnel peers, which then install those prefixes into their WireGuard peer configuration. This allows a malicious authenticated workspace agent to advertise IP prefixes it does not legitimately own, including another agent's tailnet address, resulting in route hijacking within the tailnet. Fixed versions add validation of each AllowedIPs prefix against the authenticating agent's UUID, matching the existing validation model for Addresses. Affected versions include Coder >= 2.34.0 and < 2.34.2, >= 2.33.0 and < 2.33.8, >= 2.30.0 and < 2.32.7, and the affected 2.29 release line prior to the patched ESR release.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
AllowedIPs prefixes and hijack traffic intended for other tailnet destinations. This can enable interception of web terminal and workspace application traffic, delivery of spoofed content, and unauthorized access to sensitive traffic flows within the overlay network. The issue affects confidentiality and integrity; availability impact is not emphasized in the provided content.If you can’t patch tonight, do this now.
AllowedIPs prefixes. Investigate any agent claiming prefixes inconsistent with its authenticated UUID or expected tailnet assignment.Patch, then assume compromise.
AllowedIPs prefix against the authenticating agent's UUID. The advisory identifies patched versions as v2.34.2 for the 2.34 release line, v2.33.8 for 2.33, v2.32.7 for 2.32, and v2.29.17 for the 2.29 ESR line.No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.