CVE-2026-55428: Coder Route Hijacking Through Lack Of Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-wrq8-fcv5-8hvp",
  "modified" : "2026-07-06T20:58:30Z",
  "published" : "2026-07-06T20:58:30Z",
  "aliases" : [ "CVE-2026-55428" ],
  "summary" : "Coder: Route hijacking through lack of validation of agent-supplied AllowedIPs in tailnet coordinator",
  "details" : "### Summary\n\nThe 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.\n\n### Impact\n\nA 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.\n\n### Patches\n\nThe fix validates each `AllowedIPs` prefix against the authenticating agent's UUID just like `Addresses`.\n\nThe fix was backported to all supported release lines:\n\n| Release line | Patched version |\n|---|---|\n| 2.34 | [v2.34.2](https://github.com/coder/coder/releases/tag/v2.34.2) |\n| 2.33 | [v2.33.8](https://github.com/coder/coder/releases/tag/v2.33.8) |\n| 2.32 | [v2.32.7](https://github.com/coder/coder/releases/tag/v2.32.7) |\n| 2.29 (ESR) | [v2.29.17](https://github.com/coder/coder/releases/tag/v2.29.17) |\n\n### Workarounds\n\nOperators who cannot upgrade immediately should monitor coordinator logs for agents advertising unexpected `AllowedIPs` prefixes.\n\n### Resources\n\n- Fix: #26144\n\n### Credits\n\nCoder would like to thank Anthropic's Security Team (ANT-2026-22451) for independently disclosing this issue!",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.34.0"
      }, {
        "fixed" : "2.34.2"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.33.0"
      }, {
        "fixed" : "2.33.8"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.30.0"
      }, {
        "fixed" : "2.32.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/coder/coder/v2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.29.17"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/security/advisories/GHSA-wrq8-fcv5-8hvp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/coder/coder/pull/26144"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/coder/coder"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-285", "CWE-863" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-06T20:58:30Z",
    "nvd_published_at" : null
  }
}