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.

Affected: Packagist: dompdf/dompdf

**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…

Affected: Ubuntu:Pro:16.04:LTS: php-dompdf, Ubuntu:Pro:18.04:LTS: php-dompdf, Ubuntu:20.04:LTS: php-dompdf, Ubuntu:22.04:LTS: php-dompdf

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.