CVE-2026-32947: Step security/harden runner Egress Policy Bypass Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-46g3-37rh-v698",
  "modified" : "2026-03-20T21:21:35Z",
  "published" : "2026-03-17T18:38:16Z",
  "aliases" : [ "CVE-2026-32947" ],
  "summary" : "Egress Policy Bypass via DNS over HTTPS (DoH) in Harden-Runner (Community Tier)",
  "details" : "## Summary\n\nA vulnerability exists in the Community Tier of Harden-Runner that allows bypassing the `egress-policy: block` network restriction using DNS over HTTPS (DoH).\n\nHarden-Runner secures GitHub Actions workflows on runners by applying network policies, including an `allowed-endpoints` configuration that limits outbound traffic to specified domains and ports (e.g., `github.com:443`). In `egress-policy: block` mode, non-compliant connections are intercepted and denied. \n\nThis vulnerability exploits DoH, a protocol that encapsulates DNS queries within HTTPS requests. By crafting a DNS query that embeds exfiltrated data as a subdomain (e.g., encoding the runner's hostname into a label), an attacker can route the request through a permitted HTTPS endpoint like `dns.google` (`8.8.8.8`'s DoH service). The resolver processes the query and forwards it to the attacker's controlled domain, achieving exfiltration without directly accessing the blocked destination. This evades Harden-Runner's domain-based filtering, as the initial HTTPS connection appears legitimate. \n\nThis vulnerability requires the attacker to already have code execution capabilities within the GitHub Actions workflow.\n\nThe Enterprise Tier of Harden-Runner is **not affected** by this vulnerability.\n\n## Impact\n\nWhen Harden-Runner is configured with `egress-policy: block` and a restrictive `allowed-endpoints` list, an attacker with existing code execution capabilities within a GitHub Actions workflow can bypass the allowed domains check via DNS over HTTPS by proxying DNS queries through a permitted resolver (e.g., Google's DoH service). This allows data exfiltration even when `allowed-endpoints` is set to only whitelisted domains.\n\nThis vulnerability affects only the Community Tier. It requires the attacker to already have code execution capabilities within the GitHub Actions workflow.\n\n## Remediation\n\n### For Community Tier Users\n\nUpgrade to Harden-Runner v2.16.0 or later. \n\n### For Enterprise Tier Users\n\nNo action required. Enterprise tier customers are not affected by this vulnerability.\n\n## Credit \n\nWe would like to thank [Devansh Batham](https://github.com/devanshbatham) for responsibly disclosing this vulnerability through our security reporting process.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "GitHub Actions",
      "name" : "step-security/harden-runner"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.16.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 2.15.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/step-security/harden-runner/security/advisories/GHSA-46g3-37rh-v698"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-32947"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/step-security/harden-runner"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/step-security/harden-runner/releases/tag/v2.16.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-693", "CWE-863" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-17T18:38:16Z",
    "nvd_published_at" : "2026-03-20T05:16:13Z"
  }
}