CVE-2026-40281: Gotenberg PDF API — ExifTool Metadata Command Injection (CVSS 10)

Executive Summary

CVE-2026-40281 is a critical (CVSS 10.0) command injection vulnerability in Gotenberg — a Docker-powered stateless API widely used to generate, convert, and manipulate PDF files in CI/CD pipelines, document automation workflows, and microservice architectures. The flaw resides in the metadata write endpoint, which sanitizes metadata keys for control characters but leaves metadata values entirely unsanitized.

An attacker can embed a newline character (\n) inside a metadata value, which splits the ExifTool stdin argument stream into two separate commands, allowing arbitrary ExifTool arguments — and through ExifTool's feature set, arbitrary OS command execution — to be injected.

Given Gotenberg's prevalence in containerized document processing workflows and its typical deployment with access to file systems and downstream services, successful exploitation can result in full container compromise and potential host escape depending on container security configuration.

Vulnerability Overview

Affected Products

Technical Analysis

Background: Gotenberg and ExifTool

Gotenberg is a stateless, containerized REST API that wraps tools like Chromium, LibreOffice, and ExifTool to provide document conversion and processing services. Its metadata write endpoint allows API callers to embed metadata (author, title, subject, keywords, etc.) into generated or converted PDF files.

ExifTool — the underlying metadata manipulation tool — accepts its operation parameters via stdin when Gotenberg passes them programmatically. Each metadata key-value pair is transmitted as a separate line in stdin, with ExifTool parsing each line as a distinct argument.

Root Cause: Unsanitized Metadata Values

The Gotenberg metadata write endpoint validates keys for control characters (such as newlines), preventing key-level injection. However, the corresponding value sanitization is absent — values are passed to ExifTool's stdin without stripping or escaping control characters.

Vulnerable input:
  metadata_key = "Author"
  metadata_value = "Attacker\n-execute=<payload>"

ExifTool stdin (split by newline):
  Line 1: -Author=Attacker
  Line 2: -execute=<payload>    ← injected ExifTool argument

The -execute option in ExifTool allows arbitrary Perl code execution, effectively enabling OS command execution in the container environment.

Exploit Path

1. Attacker sends POST request to Gotenberg metadata write endpoint
2. Metadata value contains embedded \n followed by -execute=<perl_payload>
3. Gotenberg passes unsanitized value to ExifTool via stdin
4. ExifTool receives two stdin lines: the legitimate metadata argument and the injected -execute argument
5. ExifTool executes the injected Perl payload
6. Arbitrary code runs in the Gotenberg container context

Exploitation Complexity

Because many Gotenberg deployments are internal microservices without authentication, exploitation may require no credentials at all — only network access to the Gotenberg API port (default: 3000). This drives the CVSS score to 10.0.

In environments where Gotenberg is exposed via an internet-facing API gateway or ingress controller without authentication, the attack surface is public.

Impact Assessment

Immediate Remediation

Step 1: Upgrade Gotenberg

# Pull the patched image
docker pull gotenberg/gotenberg:8.31.0
 
# Update docker-compose.yml
services:
  gotenberg:
    image: gotenberg/gotenberg:8.31.0  # was 8.30.1 or earlier
    ...
 
# Redeploy
docker compose up -d gotenberg

Step 2: Verify Current Version

# Check running Gotenberg version
docker inspect gotenberg/gotenberg:latest | grep -i version
 
# Or check via health endpoint
curl http://localhost:3000/health

Step 3: Restrict API Access While Patching

If immediate upgrade is not possible, restrict Gotenberg API access to trusted internal callers only:

# Nginx example: restrict Gotenberg to internal subnets
location /forms/pdfengines/metadata {
    allow 10.0.0.0/8;
    allow 172.16.0.0/12;
    deny all;
}

Step 4: Review Container Security Posture

# Ensure Gotenberg is NOT running in privileged mode
docker inspect <gotenberg-container> | grep -i privileged
 
# Verify no unnecessary host mounts
docker inspect <gotenberg-container> | grep -A 5 '"Mounts"'
 
# Check container user — should not be root
docker exec <gotenberg-container> whoami

Step 5: Audit API Logs for Exploitation Indicators

# Look for metadata values containing newline-encoded sequences
grep -E "(%0a|%0A|\\\\n)" /var/log/nginx/gotenberg-access.log
 
# Check Gotenberg container logs for anomalous ExifTool invocations
docker logs gotenberg 2>&1 | grep -i "exiftool"

Detection Indicators

Post-Remediation Checklist

1. Upgrade Gotenberg to version 8.31.0 or later
2. Audit API access controls — ensure Gotenberg is not internet-accessible without authentication
3. Implement API authentication — add an API gateway with authentication in front of Gotenberg
4. Review container security — disable privileged mode, minimize host mounts, run as non-root
5. Scan historical API logs for exploitation artifacts (newline-encoded metadata values)
6. Check downstream systems — if exploitation occurred, treat all services accessible from the Gotenberg container as potentially compromised
7. Rotate secrets — refresh all environment variables and mounted secrets accessible to the container
8. Consider network policies — Kubernetes NetworkPolicy or equivalent to restrict egress from Gotenberg pods

References

• NVD — CVE-2026-40281
• Gotenberg GitHub Repository
• ExifTool Documentation — -execute option
• OWASP — Command Injection