CVE-2021-21707 is a medium-severity vulnerability affecting PHP versions 7.3.x before 7.3.33, 7.4.x before 7.4.26, and 8.0.x before 8.0.13. This vulnerability allows certain XML parsing functions, such as simplexml_load_file(), to URL-decode the filename passed to them. If the filename includes a URL-encoded NUL character, it may cause the function to misinterpret the filename, resulting in the potential reading of unintended files. The CVSS score for this vulnerability is 5.3, indicating a medium severity level. Organizations using affected PHP versions are at risk of unauthorized file access.
The risk to organizations includes potential exposure of sensitive information, as attackers may leverage this vulnerability to access files that should remain protected. The vulnerability has been acknowledged by the PHP development team and is classified as modified in its status. Given the potential for exploitation, it is crucial for organizations to prioritize patching for the affected PHP versions immediately.
The vulnerability was published on November 29, 2021. While there is currently no known public exploit, it is essential for organizations to remain vigilant and apply the latest security updates. The exploitability score for this vulnerability is rated medium, indicating that while it may not be trivial to exploit, the risk remains significant.
In light of the risks associated with CVE-2021-21707, organizations should assess their PHP deployment and apply necessary patches to mitigate any potential threats. Ensuring that systems are updated to the latest versions will help protect against this and similar vulnerabilities.
Vulnerability Details
The official description of CVE-2021-21707 indicates that in PHP versions 7.3.x below 7.3.33, 7.4.x below 7.4.26, and 8.0.x below 8.0.13, certain XML parsing functions, like simplexml_load_file(), URL-decode the filename passed to them. If that filename contains a URL-encoded NUL character, this may cause the function to interpret this as the end of the filename, leading to unintended file access.
The CVSS score for this vulnerability is 5.3, categorized as medium severity. The vulnerability is classified under CWE-159. The affected products include PHP, clustered_data_ontap, debian_linux, and tenable.sc.
Technical Analysis
The root cause of CVE-2021-21707 lies in the improper handling of URL-encoded filenames during XML parsing. Attackers may exploit this vulnerability by crafting a malicious filename containing a URL-encoded NUL character, which leads to incorrect interpretation of the filename by the PHP functions. The attack vector is network-based, and the complexity of the attack is low, requiring no privileges or user interaction.
In terms of impacts, the confidentiality impact is low, as unauthorized file access may expose sensitive data. However, there is no integrity or availability impact associated with this vulnerability. Organizations should ensure that their systems are configured to validate and sanitize user input effectively.
Risk & Impact Analysis
The real-world deployment risk associated with CVE-2021-21707 is significant, especially for organizations utilizing PHP in web applications. The potential for unauthorized file access could lead to data breaches, impacting customer trust and regulatory compliance. The blast radius of this vulnerability extends to any application relying on vulnerable PHP versions, making it a critical issue for organizations in various sectors.
Organizations should assess the urgency of addressing this vulnerability based on its CVSS score and the potential impact on their operations. Given the medium severity classification, organizations should address it in their priority patch cycle to prevent exploitation.
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions for CVE-2021-21707 include PHP versions 7.3.x below 7.3.33, 7.4.x below 7.4.26, and 8.0.x below 8.0.13. Additionally, it affects clustered_data_ontap and debian_linux versions 10.0 and 11.0, as well as tenable.sc versions prior to 5.21.0. Organizations should apply patches or upgrades to mitigate this vulnerability.
Mitigation & Remediation
To remediate CVE-2021-21707, organizations should ensure they upgrade to the latest PHP versions, specifically 7.3.33, 7.4.26, and 8.0.13 or later. In addition to upgrading, organizations should review their XML parsing code to ensure proper handling of filenames and implement strict validation checks for user input. This includes sanitizing filenames before processing them in XML functions.
Organizations should monitor their systems for any unusual file access patterns and consider implementing network controls to restrict access to sensitive files. For further security assessments, organizations may consider engaging in penetration testing services to identify vulnerabilities in their systems.
Detection Guidance
To detect potential exploitation of CVE-2021-21707, organizations should monitor system logs for indicators of unauthorized file access. Look for unusual patterns in file access logs that may indicate attempts to read sensitive files. Additionally, monitor for behavioral anomalies in applications that utilize XML parsing functions.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2021-21707 highlights the need for organizations to implement robust validation mechanisms to prevent similar vulnerabilities in the future. This incident reflects a broader trend in software vulnerabilities where improper handling of user input can lead to critical security issues.
Security teams should prioritize ongoing education and training regarding secure coding practices. Organizations are encouraged to review their current security posture and ensure they are prepared to respond to vulnerabilities quickly and effectively. For more information on best practices, refer to our penetration testing methodology and vulnerability management program resources.
As the landscape of vulnerabilities continues to evolve, it is imperative that organizations stay informed and proactive in their security efforts, ensuring they can withstand potential threats posed by vulnerabilities such as CVE-2021-21707.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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