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Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists

Type: advisorySources: OSV

Gotenberg is an API-based document conversion tool. In versions 8.30.1 and earlier, the default private-IP deny-lists for the --webhook-deny-list and --api-download-from-deny-list flags use a case-sensitive regular expression (^https?://) to match URL schemes. Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://). This allows unauthenticated requests to reach internal network services, including private IP ranges, loopback addresses, and cloud instance metadata endpoints such as HTTP://169.254.169.254/latest/meta-data/. This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.

Products
Not specified
Affected versions
Not specified
Fixed versions
Not specified
CVEs
CVE-2026-40280
Confirmed fixed CVEs
Not specified
Updated in this feed
2 Nov 2026, 20:36 UTC · Revision 1

Source evidence

Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists

core-osv · Original source

Published 5 May 2026, 19:52 UTC

Gotenberg is an API-based document conversion tool. In versions 8.30.1 and earlier, the default private-IP deny-lists for the --webhook-deny-list and --api-download-from-deny-list flags use a case-sensitive regular expression (^https?://) to match URL schemes. Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://). This allows unauthenticated requests to reach internal network services, including private IP ranges, loopback addresses, and cloud instance metadata endpoints such as HTTP://169.254.169.254/latest/meta-data/. This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.

osv:CVE-2026-40280
Complete source record
{
  "id": "ee85a36050ed65fdc4073c666f6a2fa330c6575d07a217db34d0af752a34c502",
  "url": "https://osv.dev/vulnerability/CVE-2026-40280",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Gotenberg SSRF via case-insensitive URL scheme bypass in webhook and downloadFrom deny-lists",
    "summary": "Gotenberg is an API-based document conversion tool. In versions 8.30.1 and earlier, the default private-IP deny-lists for the --webhook-deny-list and --api-download-from-deny-list flags use a case-sensitive regular expression (^https?://) to match URL schemes. Because Go's net/url.Parse() normalizes the scheme to lowercase before establishing the outbound TCP connection, an attacker can bypass the deny-list by simply capitalizing part of the URL scheme (e.g., HTTP://, HTTPS://, or Http://). This allows unauthenticated requests to reach internal network services, including private IP ranges, loopback addresses, and cloud instance metadata endpoints such as HTTP://169.254.169.254/latest/meta-data/. This bypasses the same security control that was patched in CVE-2026-27018. This issue has been fixed in version 8.31.0.",
    "evidence": "osv:CVE-2026-40280",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-40280",
      "aliases": [
        "CVE-2026-40280",
        "GHSA-5q7p-7jgv-ww56",
        "GO-2026-5151"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/gotenberg/gotenberg",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "db51f9026d13357aecc23e3c99ba6937ac09fbfc"
                },
                {
                  "fixed": "3f01ca18d3cc21375a1e2da4b5a3f261c8548e47"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:thecodingmachine:gotenberg:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "8.31.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "3f01ca18d3cc21375a1e2da4b5a3f261c8548e47"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v8.30.1",
            "v8.30.0",
            "v8.29.1",
            "v8.29.0",
            "v8.28.0",
            "v8.27.0",
            "v8.26.0",
            "v8.25.1",
            "v8.25.0",
            "v8.24.0",
            "v8.23.2",
            "v8.23.1",
            "v8.23.0",
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            "v8.21.0",
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            "v8.14.0",
            "v8.13.0",
            "v8.12.0",
            "v8.11.1",
            "v8.11.0",
            "v8.10.0",
            "v8.9.2",
            "v8.9.1",
            "v8.9.0",
            "v8.8.1",
            "v8.8.0",
            "v8.7.0",
            "v8.6.0",
            "v8.5.1",
            "v8.5.0",
            "v8.4.0",
            "v8.3.0",
            "v8.2.2",
            "v8.2.1",
            "v8.2.0",
            "v8.1.0",
            "v8.0.3",
            "v8.0.2",
            "v8.0.1",
            "v8.0.0",
            "v7.10.1",
            "v7.10.0",
            "v7.9.2",
            "v7.9.1",
            "v7.9.0",
            "v7.8.3",
            "v7.8.2",
            "v7.8.1",
            "v7.8.0",
            "v7.7.2",
            "v7.7.1",
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            "v7.4.2",
            "v7.4.1",
            "v7.4.0",
            "v7.3.1",
            "v7.3.0",
            "v7.2.0",
            "v7.1.1",
            "v7.1.0",
            "v7.0.7",
            "v7.0.6",
            "v7.0.5",
            "v7.0.4",
            "v7.0.3",
            "v7.0.2",
            "v7.0.1",
            "v7.0.0",
            "6.4.4",
            "6.4.3",
            "6.4.2",
            "6.4.1",
            "6.4.0",
            "6.3.1",
            "6.3.0",
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            "6.1.2",
            "6.1.1",
            "6.1.0",
            "6.0.4",
            "6.0.3",
            "6.0.2",
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            "6.0.0",
            "5.1.0",
            "5.0.2",
            "5.0.1",
            "5.0.0",
            "4.4.0",
            "4.3.0",
            "4.2.0",
            "4.1.0",
            "4.0.0",
            "3.2.0",
            "3.1.2",
            "3.1.1",
            "3.1.0",
            "3.0.2",
            "3.0.1",
            "3.0.0",
            "2.0.0",
            "1.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-40280.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.407884953Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40280.json",
        "https://github.com/advisories/GHSA-jjwv-57xh-xr6r",
        "https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-40280",
        "https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-918"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/40xxx/CVE-2026-40280.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-40280",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489940,
  "published_at": "2026-05-05T19:52:40.327+00:00"
}