CVE-2023-41330: knplabs/knp-snappy is a PHP library allowing thumbnail, snapshot or PDF generation from a url or a html page. ## Issue On March 17th the vulnerability…

knplabs/knp-snappy is a PHP library allowing thumbnail, snapshot or PDF generation from a url or a html page.
## Issue

On March 17th the vulnerability CVE-2023-28115 was disclosed, allowing an attacker to gain remote code execution through PHAR deserialization. Version 1.4.2 added a check `if (\strpos($filename, 'phar://') === 0)` in the `prepareOutput` function to resolve this CVE, however if the user is able to control the second parameter of the `generateFromHtml()` function of Snappy, it will then be passed as the `$filename` parameter in the `prepareOutput()` function. In the original vulnerability, a file name with a `phar://` wrapper could be sent to the `fileExists()` function, equivalent to the `file_exists()` PHP function. This allowed users to trigger a deserialization on arbitrary PHAR files. To fix this issue, the string is now passed to the `strpos()` function and if it starts with `phar://`, an exception is raised. However, PHP wrappers being case insensitive, this patch can be bypassed using `PHAR://` instead of `phar://`. A successful exploitation of this vulnerability allows executing arbitrary code and accessing the underlying filesystem. The attacker must be able to upload a file and the server must be running a PHP version prior to 8. This issue has been addressed in commit `d3b742d61a` which has been included in version 1.4.3. Users are advised to upgrade. Users unable to upgrade should ensure that only trusted users may submit data to the `AbstractGenerator->generate(...)` function.

Affected

Detection & IOCsextracted from sources · hover to see the quote

• →Detect PHAR wrapper bypass via case-insensitive variants (e.g., PHAR://) passed as the second parameter to generateFromHtml() or as $filename in prepareOutput() ↗
• →Monitor for PHAR deserialization attempts via file_exists()-equivalent calls (fileExists()) with attacker-controlled filenames containing phar:// or PHAR:// wrappers ↗
• →Flag exploitation attempts where user-controlled input reaches AbstractGenerator->generate(...) with PHAR-scheme filenames ↗
• →Exploitation requires a prior file upload step; correlate suspicious file uploads with subsequent PHAR deserialization triggers on PHP versions prior to 8 ↗

• ·Exploitation is limited to PHP versions prior to 8; environments running PHP 8+ are not affected by this specific PHAR deserialization vector ↗

CVSS provenance