CVE-2023-41330
CVE-2023-41330
Weakness (CWE)
CVSS Vector
v3.1- Attack Vector
- Network
- Attack Complexity
- Low
- Privileges Required
- None
- User Interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Description
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.
Comprehensive Technical Analysis of CVE-2023-41330
1. Vulnerability Assessment and Severity Evaluation
CVE ID: CVE-2023-41330 CVSS Score: 9.8
Severity Evaluation: The CVSS score of 9.8 indicates a critical vulnerability. This high score is due to the potential for remote code execution (RCE) and unauthorized access to the underlying filesystem, which can lead to significant security breaches.
Vulnerability Assessment:
The vulnerability arises from an incomplete fix for a previous issue (CVE-2023-28115) in the knplabs/knp-snappy PHP library. The initial patch attempted to prevent PHAR deserialization by checking if the filename starts with phar://. However, due to PHP wrappers being case insensitive, the check can be bypassed using PHAR:// or other case variations.
2. Potential Attack Vectors and Exploitation Methods
Attack Vectors:
- File Upload: An attacker could upload a malicious file with a
PHAR://wrapper. - User Input: If the user can control the second parameter of the
generateFromHtml()function, they can pass a filename with aPHAR://wrapper. - Deserialization: The malicious file can trigger PHAR deserialization, leading to arbitrary code execution.
Exploitation Methods:
- PHAR Deserialization: By exploiting the case insensitivity of PHP wrappers, an attacker can bypass the
strpos()check and trigger deserialization. - Arbitrary Code Execution: Once deserialization occurs, the attacker can execute arbitrary code on the server.
- Filesystem Access: The attacker can access and manipulate the underlying filesystem, potentially leading to data exfiltration or system compromise.
3. Affected Systems and Software Versions
Affected Systems:
- Systems running PHP versions prior to 8.0.
- Systems using the
knplabs/knp-snappylibrary versions 1.4.2 and earlier.
Software Versions:
knplabs/knp-snappyversions prior to 1.4.3.
4. Recommended Mitigation Strategies
Immediate Mitigation:
- Upgrade: Upgrade to
knplabs/knp-snappyversion 1.4.3 or later, which includes the fix for this vulnerability. - Input Validation: Ensure that only trusted users can submit data to the
AbstractGenerator->generate(...)function. - File Upload Restrictions: Implement strict validation and sanitization for file uploads to prevent malicious files from being processed.
Long-Term Mitigation:
- Regular Updates: Keep all software dependencies up to date to benefit from the latest security patches.
- Security Audits: Conduct regular security audits and code reviews to identify and mitigate potential vulnerabilities.
- Least Privilege: Implement the principle of least privilege to minimize the impact of potential exploits.
5. Impact on Cybersecurity Landscape
Immediate Impact:
- Organizations using the affected versions of
knplabs/knp-snappyare at high risk of RCE and filesystem access attacks. - The vulnerability highlights the importance of thorough testing and validation of security patches.
Long-Term Impact:
- Increased awareness of the risks associated with PHAR deserialization and the need for robust input validation.
- Emphasis on the importance of case-sensitive checks in security-critical code.
6. Technical Details for Security Professionals
Vulnerability Details:
- The vulnerability is due to an incomplete fix for CVE-2023-28115, which allowed PHAR deserialization through the
phar://wrapper. - The patch in version 1.4.2 added a check
if (\strpos($filename, 'phar://') === 0), but this can be bypassed usingPHAR://due to PHP's case insensitivity.
Code Analysis:
- The
prepareOutputfunction inknplabs/knp-snappyprocesses the filename parameter. - The
generateFromHtml()function can be manipulated to pass a filename with aPHAR://wrapper, bypassing thestrpos()check.
Patch Details:
- The fix is included in commit
d3b742d61aand version 1.4.3. - The patch likely involves a more robust check that accounts for case insensitivity, ensuring that all variations of the
phar://wrapper are blocked.
References:
Conclusion: CVE-2023-41330 is a critical vulnerability that underscores the importance of thorough security testing and the need for robust input validation. Organizations should prioritize upgrading to the patched version and implementing additional security measures to mitigate the risk of similar vulnerabilities in the future.