Gotenberg is a Docker-powered stateless API for PDF files. Prior to 8.31.0, Gotenberg's /forms/pdfengines/metadata/write HTTP endpoint accepts a JSON metadata object and passes its keys directly to ExifTool via the go-exiftool library. No validation is performed on key characters. A \n embedded in a JSON key splits the ExifTool stdin stream into a new argument line, allowing an attacker to inject arbitrary ExifTool flags — including -if, which evaluates Perl expressions. This achieves unauthenticated OS command execution in a single HTTP request. The response is HTTP 200 with a valid PDF, making the attack transparent to basic monitoring. This vulnerability is fixed in 8.31.0.

Affected: Go: github.com/gotenberg/gotenberg/v8

# Unauthenticated RCE in Gotenberg via Metadata Key Newline Injection

## Summary

Gotenberg's `/forms/pdfengines/metadata/write` HTTP endpoint accepts a JSON metadata object and passes its keys directly to ExifTool via the go-exiftool library. No validation is performed on key characters. A `\n` embedded in a JSON key splits the ExifTool stdin stream into a new argument line, allowing an attacker to inject arbitrary ExifTool flags — including `-if`, which evaluates Perl expressions. This achieves unauthenticated OS command execution in a single HTTP request. The response is HTTP 200 with a valid PDF, making the attack transparent to basic monitoring.

## Vulnerability Details

| Field | Value | |------------------|------------------------------------------| | Product | Gotenberg | | Version | 8.29.1 (default `gotenberg/gotenberg:8`) | | Component | `pdfengines/metadata/write` endpoint | | CWE | CWE-78 — Improper Neutralization of Special Elements used in an OS Command |

## Affected Code

**Product:** Gotenberg **Endpoint:** `/forms/pdfengines/metadata/write` **Root cause:** JSON metadata keys are passed to go-exiftool without control-character validation. The existing `dangerousTags` blocklist uses exact-match deletion and provides no defense against `\n`-embedded keys.

The injection occurs because go-exiftool writes each key to ExifTool's stdin as:…