CVE-2023-23924 is a critical-severity (CVSS 10) CWE-551 vulnerability in dompdf/dompdf. 3 public exploit or proof-of-concept references are indexed, so weaponization risk is real. A fix is available for dompdf/dompdf — see the affected versions and patch details below.
URI validation failure on SVG parsing in Dompdf
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-23924.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
dompdf/dompdfReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | dompdf/dompdf | all versions | 2.0.2composer require dompdf/dompdf:^2.0.2 |
Affected Products
dompdfdompdf_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompdf/dompdf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dompdf/dompdf to 2.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-23924 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.
Frequently Asked Questions
Is CVE-2023-23924 in your dependencies?
Find it across Packagist, including transitive dependencies.