GHSA-3cw5-7cxw-v5qg

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Source
https://github.com/advisories/GHSA-3cw5-7cxw-v5qg
Import Source
https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2023/02/GHSA-3cw5-7cxw-v5qg/GHSA-3cw5-7cxw-v5qg.json
JSON Data
https://api.osv.dev/v1/vulns/GHSA-3cw5-7cxw-v5qg
Aliases
Published
2023-02-01T01:37:56Z
Modified
2023-11-08T04:11:42.657197Z
Severity
  • 10.0 (Critical) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:H CVSS Calculator
Summary
Dompdf vulnerable to URI validation failure on SVG parsing
Details

Summary

The URI validation on dompdf 2.0.1 can be bypassed on SVG parsing by passing <image> 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 <image> 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 <image> 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 :

<svg>
    <Image xlink:href="phar:///foo"></Image>
</svg>

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 :

<svg>
    <Image xlink:href="phar:///foo"></Image>
</svg>

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.

References

Affected packages

Packagist / dompdf/dompdf

Package

Name
dompdf/dompdf
Purl
pkg:composer/dompdf/dompdf

Affected ranges

Type
ECOSYSTEM
Events
Introduced
0Unknown introduced version / All previous versions are affected
Fixed
2.0.2

Affected versions

v0.*

v0.6.0
v0.6.1
v0.6.2
v0.7.0-beta
v0.7.0-beta2
v0.7.0-beta3
v0.7.0
v0.8.0
v0.8.1
v0.8.2
v0.8.3
v0.8.4
v0.8.5
v0.8.6

v1.*

v1.0.0
v1.0.1
v1.0.2
v1.1.0
v1.1.1
v1.2.0
v1.2.1
v1.2.2

v2.*

v2.0.0
v2.0.1