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githubGitHub Advisory DatabaseGHSA-3CW5-7CXW-V5QG
HistoryFeb 01, 2023 - 1:37 a.m.

Dompdf vulnerable to URI validation failure on SVG parsing

2023-02-0101:37:56
CWE-551
CWE-863
GitHub Advisory Database
github.com
24
dompdf
uri validation
svg parsing
vulnerability
php
phar url wrapper

CVSS3

10

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

HIGH

Integrity Impact

LOW

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:H

EPSS

0.01

Percentile

84.0%

Summary

The URI validation on dompdf 2.0.1 can be bypassed on SVG parsing by passing &lt;image&gt; tags with uppercase letters. This might leads to arbitrary object unserialize on PHP < 8, through the phar URL wrapper.

Details

The bug occurs during SVG parsing of &lt;image&gt; tags, in src/Image/Cache.php :

if ($type === "svg") {
    $parser = xml_parser_create("utf-8");
    xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, false);
    xml_set_element_handler(
        $parser,
        function ($parser, $name, $attributes) use ($options, $parsed_url, $full_url) {
            if ($name === "image") {
                $attributes = array_change_key_case($attributes, CASE_LOWER);

This part will try to detect &lt;image&gt; tags in SVG, and will take the href to validate it against the protocolAllowed whitelist. However, the `$name comparison with “image” is case sensitive, which means that such a tag in the SVG will pass :

&lt;svg&gt;
    &lt;Image xlink:href="phar:///foo"&gt;&lt;/Image&gt;
&lt;/svg&gt;

As the tag is named “Image” and not “image”, it will not pass the condition to trigger the check.

A correct solution would be to strtolower the $name before the check :

if (strtolower($name) === "image") {

PoC

Parsing the following SVG file is sufficient to reproduce the vulnerability :

&lt;svg&gt;
    &lt;Image xlink:href="phar:///foo"&gt;&lt;/Image&gt;
&lt;/svg&gt;

Impact

An attacker might be able to exploit the vulnerability to call arbitrary URL with arbitrary protocols, if they can provide a SVG file to dompdf. In PHP versions before 8.0.0, it leads to arbitrary unserialize, that will leads at the very least to an arbitrary file deletion, and might leads to remote code execution, depending on classes that are available.

Affected configurations

Vulners
Node
dompdfdompdfRange<2.0.2
CPENameOperatorVersion
dompdf/dompdflt2.0.2

CVSS3

10

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

NONE

Scope

CHANGED

Confidentiality Impact

HIGH

Integrity Impact

LOW

Availability Impact

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:H

EPSS

0.01

Percentile

84.0%