CVE-2021-21703 is a high-severity vulnerability affecting PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25, and 8.0.x below 8.0.12. This vulnerability allows local unprivileged users to escalate privileges to the root user. When PHP FPM SAPI operates with the main FPM daemon process running as root and child worker processes executing as lower-privileged users, the child processes can access and write to shared memory with the main process. This could lead to invalid memory reads and writes, posing a significant risk to system integrity.
The vulnerability has a CVSS score of 7.8, indicating high severity. Organizations using affected versions of PHP should prioritize patching immediately to avoid potential exploitation. The risk to organizations includes unauthorized access to sensitive data, system integrity compromise, and operational disruption due to privilege escalation.
Currently, there are no public exploits available, and it is not listed in the KEV catalog, indicating that it has not been actively exploited in the wild. However, the potential for exploitation exists, given the nature of the vulnerability and the privileges it could expose.
Organizations should address this vulnerability as part of their priority patch cycle, ensuring that all affected systems are updated to mitigate the risk effectively.
Vulnerability Details
The official description of CVE-2021-21703 states that when running PHP FPM SAPI with the main FPM daemon process as root, child processes running as lower-privileged users can access and modify shared memory. This memory manipulation can result in the root process conducting invalid memory operations, leading to privilege escalation.
This vulnerability has been assigned a CVSS score of 7.8, reflecting its high severity. The attack vector is local, requiring low privileges with no user interaction. The impacts on confidentiality, integrity, and availability are all rated as high.
The vulnerability affects PHP, Debian Linux, Fedora, NetApp's clustered Data ONTAP, and Oracle's communications diameter signaling router. It was published on October 25, 2021.
Technical Analysis
The root cause of the vulnerability relates to improper memory access and management. The attack vector is local, meaning that an attacker must have local access to the system. The attack complexity is rated as high due to the requirement for specific conditions to be exploited. While low privileges are sufficient for the attacker, no user interaction is necessary.
Once exploited, the vulnerability significantly impacts confidentiality, integrity, and availability, providing attackers with the capability to escalate privileges to root.
Risk & Impact Analysis
The real-world deployment risk associated with CVE-2021-21703 is considerable. As organizations increasingly rely on PHP for web applications and services, the potential for exploitation increases. Attackers may leverage this vulnerability to gain unauthorized access, leading to data breaches and significant operational impact.
Given its high CVSS score, organizations should assess their exposure to this vulnerability and prioritize remediation efforts. The urgency for addressing this vulnerability is high, given the potential blast radius and the implications for sensitive data and system integrity.
Organizations should prioritize patching immediately, as the risks associated with the exploitation of this vulnerability are substantial.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The affected versions for this vulnerability are PHP versions 7.3.x (up to and including 7.3.31), 7.4.x (below 7.4.25), and 8.0.x (below 8.0.12). For Debian Linux, the vulnerable versions include Debian 9.0, 10.0, and 11.0. Fedora versions 33, 34, and 35 are also impacted. NetApp's clustered Data ONTAP and Oracle's communications diameter signaling router are additionally affected.
Mitigation & Remediation
To mitigate this vulnerability, organizations should apply the relevant patches or updates provided by the respective vendors. For PHP, users should upgrade to versions that are not affected, such as 7.4.25 or higher, and 8.0.12 or higher. Additionally, organizations should implement configuration hardening and network controls to limit exposure to untrusted users.
Monitoring for unauthorized access attempts and unusual behavior in PHP applications is also recommended. For further assistance, organizations can consider engaging with AppSecure's penetration testing services to validate their security posture.
Detection Guidance
Organizations should monitor logs for indicators of unauthorized access and potential exploitation attempts. Behavioral anomalies such as unexpected child process memory access should be flagged. Additionally, network signatures indicating communication from untrusted sources should be reviewed.
AppSecure Threat Intelligence Insight
CVE-2021-21703 highlights the importance of secure memory management in multi-process environments. This vulnerability represents a pattern of misconfigurations where shared memory is not adequately protected from unauthorized access. Security teams should ensure robust privilege management and consider adopting best practices for secure coding.
For effective remediation, organizations should develop a comprehensive vulnerability management program that includes regular audits and security assessments. Additionally, leveraging insights from threat intelligence can help identify vulnerabilities early.
Engaging in proactive security measures such as penetration testing methodologies can also provide a significant advantage in identifying and mitigating vulnerabilities before they can be exploited.
Ultimately, the strategic takeaway is to maintain a continuous improvement mindset towards security posture, ensuring that all software components are regularly updated and monitored for vulnerabilities.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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