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Medium

SSRF allowlist bypass via percent-encoded host in hackney

Type: advisorySources: OSV

Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost. This issue affects hackney: from 0.13.0 before 4.0.1.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-47076
Confirmed fixed CVEs
Not specified
Updated in this feed
7 Nov 2026, 04:52 UTC · Revision 1

Source evidence

SSRF allowlist bypass via percent-encoded host in hackney

core-osv · Original source

Published 25 May 2026, 14:00 UTC

Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost. This issue affects hackney: from 0.13.0 before 4.0.1.

osv:CVE-2026-47076
Complete source record
{
  "id": "31c3a838330731c26693c1b2a3c3015bb325f011e2bf87cec23ad04d2a279eed",
  "url": "https://osv.dev/vulnerability/CVE-2026-47076",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "SSRF allowlist bypass via percent-encoded host in hackney",
    "summary": "Interpretation Conflict vulnerability in benoitc hackney allows Server Side Request Forgery. hackney_url:normalize/2 URL-decodes the host component after the URL has been parsed into a #hackney_url{} record. OTP's uri_string:parse/1 and inet:parse_address/1 do not decode percent-escapes in the host, so a URL such as http://%31%32%37%2E%30%2E%30%2E%31/ is seen by a caller's allowlist validator with host %31%32%37%2E%30%2E%30%2E%31 (not an IP address), which passes the allowlist check. hackney's normalizer then decodes the host to 127.0.0.1 and opens a TCP connection to loopback. Because hackney:request/5 always calls hackney_url:normalize/2 with no opt-out, every request that takes a binary or list URL is affected. The same technique reaches cloud instance metadata services (169.254.169.254), RFC1918 networks, and any admin interface listening on localhost. This issue affects hackney: from 0.13.0 before 4.0.1.",
    "evidence": "osv:CVE-2026-47076",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-47076",
      "aliases": [
        "CVE-2026-47076",
        "EEF-CVE-2026-47076",
        "GHSA-pj7v-xfvx-wmjq"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/benoitc/hackney",
              "type": "GIT",
              "events": [
                {
                  "introduced": "fd2158b39b0aa139bb90f0c867f246ddfec072e6"
                },
                {
                  "fixed": "c41c8d48ace8141b003f6f1de3ca6734a0c53056"
                },
                {
                  "fixed": "452620a92ec1da2e6b4862a049a2a4f04b42068f"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:benoitc:hackney:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.13.0"
                      },
                      {
                        "fixed": "4.0.1"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "452620a92ec1da2e6b4862a049a2a4f04b42068f"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "4.0.0",
            "3.2.1",
            "3.2.0",
            "3.1.2",
            "3.1.1",
            "3.1.0",
            "3.0.3",
            "3.0.2",
            "3.0.1",
            "2.0.1",
            "2.0.0",
            "2.0.0-beta.1",
            "1.25.0",
            "1.24.1",
            "1.24.0",
            "1.23.0",
            "1.22.0",
            "1.21.0",
            "1.20.1",
            "1.20.0",
            "1.19.1",
            "1.19.0",
            "1.18.2",
            "1.18.1",
            "1.18.0",
            "1.17.4",
            "1.17.3",
            "1.17.2",
            "v1.17.0",
            "1.17.0",
            "1.17.1",
            "1.16.0",
            "0.16.0",
            "1.15.2",
            "1.15.1",
            "1.15.0",
            "1.14.3",
            "1.14.2",
            "1.14.0",
            "1.13.0",
            "1.12.1",
            "1.12.0",
            "1.11.0",
            "1.10.1",
            "1.10.0",
            "1.9.0",
            "1.8.6",
            "1.8.5",
            "1.8.4",
            "1.8.3",
            "1.8.2",
            "1.8.0",
            "1.7.1",
            "1.7.0",
            "1.6.6",
            "1.6.5",
            "1.6.4",
            "1.6.3",
            "1.6.2",
            "1.6.1",
            "1.6.0",
            "1.5.7",
            "1.5.6",
            "1.5.5",
            "1.5.4",
            "1.5.1",
            "1.5.0",
            "1.4.10",
            "1.4.9",
            "1.4.8",
            "1.4.7",
            "1.4.6",
            "1.4.5",
            "1.4.4",
            "1.4.3",
            "1.4.2",
            "1.4.1",
            "1.4.0",
            "1.3.2",
            "1.3.1",
            "1.3.0",
            "1.2.0",
            "1.1.0",
            "1.0.6",
            "1.0.5",
            "1.0.4",
            "1.0.3",
            "1.0.2",
            "1.0.1",
            "1.0.0",
            "0.15.2",
            "0.15.1",
            "0.15.0",
            "0.14.3",
            "0.14.2",
            "0.14.1",
            "0.14.0",
            "0.13.1",
            "0.13.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-47076.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:49.993589902Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-47076.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-47076",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47076.json",
        "https://github.com/benoitc/hackney/security/advisories/GHSA-pj7v-xfvx-wmjq",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-47076",
        "https://github.com/benoitc/hackney/commit/452620a92ec1da2e6b4862a049a2a4f04b42068f",
        "https://github.com/benoitc/hackney"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-436",
          "CWE-918"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/47xxx/CVE-2026-47076.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-47076",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 518284,
  "published_at": "2026-05-25T14:00:46.707+00:00"
}