CVE-2022-41922 is a vulnerability affecting versions of the yiisoft Yii PHP framework prior to 1.1.27. The root cause is improper handling of untrusted data during deserialization, specifically when the application calls PHP's native unserialize() function on user-supplied input without adequate validation or sanitization. This vulnerability is classified under CWE-502: Deserialization of Untrusted Data. Exploiting this flaw allows an attacker to perform Remote Code Execution (RCE) by crafting malicious serialized payloads that, when unserialized by the vulnerable application, can trigger execution of arbitrary PHP code. The vulnerability arises because unserialize() can instantiate arbitrary PHP objects and invoke their magic methods, which may contain exploitable code paths. The patch in version 1.1.27 addresses this by preventing unsafe unserialization or by implementing safer deserialization mechanisms. No known public exploits have been reported in the wild as of the publication date, but the vulnerability remains critical due to the potential impact of RCE. The vulnerability requires that the application explicitly calls unserialize() on attacker-controlled input, which is a common but unsafe practice in PHP applications. The attack does not require authentication but does require the attacker to supply crafted serialized data to the vulnerable endpoint or input vector. This vulnerability is particularly relevant for web applications built on Yii framework versions prior to 1.1.27 that handle serialized data from users, such as session data, cookies, or API inputs.

For European organizations using vulnerable versions of the Yii framework, this vulnerability poses a significant risk of remote code execution, which can lead to full system compromise, data breaches, and disruption of services. Attackers could leverage this flaw to execute arbitrary commands on web servers, potentially gaining access to sensitive data, deploying malware, or pivoting within internal networks. This is especially critical for sectors handling sensitive personal data under GDPR, such as finance, healthcare, and government services. The ability to execute code remotely without authentication increases the attack surface and lowers the barrier for exploitation. If exploited, organizations may face operational downtime, reputational damage, regulatory penalties, and financial losses. Given the widespread use of Yii in web applications across Europe, the vulnerability could affect a broad range of industries. However, the actual impact depends on whether the application uses unserialize() on untrusted input, which is a development practice rather than a default framework behavior. Organizations with legacy or custom Yii applications are at higher risk.

1. Immediate upgrade: Organizations should upgrade all Yii framework instances to version 1.1.27 or later, where the vulnerability is patched. 2. Code audit: Review application code to identify any use of unserialize() on user-controlled input and refactor to avoid unserialization of untrusted data. 3. Input validation: Implement strict validation and sanitization of any serialized data received from clients before deserialization. 4. Use safer alternatives: Replace PHP's native unserialize() with safer deserialization libraries or JSON-based serialization where possible. 5. Web application firewall (WAF): Deploy and configure WAF rules to detect and block suspicious serialized payloads targeting unserialize() endpoints. 6. Monitoring and logging: Enhance logging around deserialization functions and monitor for anomalous inputs or errors indicative of exploitation attempts. 7. Incident response readiness: Prepare for potential exploitation by having response plans and backups in place. 8. Developer training: Educate developers on secure deserialization practices and the risks of unserialize() on untrusted data. These mitigations go beyond generic patching by emphasizing secure coding practices and proactive detection.