CVE-2021-24857 in ToTop Link Plugin
Summary
by MITRE • 12/13/2021
The ToTop Link WordPress plugin through 1.7.1 passes base64 encoded user input to the unserialize() PHP function, which could lead to PHP Object injection if a plugin installed on the blog has a suitable gadget chain.
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Analysis
by VulDB Data Team • 12/15/2021
The CVE-2021-24857 vulnerability resides within the ToTop Link WordPress plugin version 1.7.1 and earlier, presenting a critical security risk through improper input handling and deserialization practices. This flaw allows malicious actors to exploit a PHP object injection vulnerability by leveraging base64 encoded user input that gets passed directly to the unserialize() function. The vulnerability's severity stems from the fact that it creates a pathway for arbitrary code execution when combined with existing gadget chains present in other installed plugins, making it particularly dangerous in environments where multiple plugins are deployed.
The technical implementation of this vulnerability involves the plugin's failure to properly sanitize or validate user input before processing it through PHP's unserialize() function. When user-supplied data is base64 encoded and subsequently passed to unserialize(), it creates an opportunity for attackers to craft malicious serialized objects that can execute arbitrary code on the target system. This particular flaw aligns with CWE-502, which describes the weakness of deserializing untrusted data, and represents a classic PHP object injection vulnerability. The vulnerability's exploitation requires the presence of suitable gadget chains within other installed plugins, as the attacker must leverage existing deserialization gadgets to achieve full compromise.
From an operational standpoint, this vulnerability poses significant risks to WordPress installations using the affected plugin, particularly in multi-plugin environments where other vulnerable components may exist. The impact extends beyond simple data compromise to potentially full system takeover, as successful exploitation can lead to remote code execution and persistent backdoor access. Attackers can leverage this vulnerability to gain unauthorized access to the web server, potentially escalating privileges and establishing persistent presence within the network. The attack vector is particularly concerning because it requires minimal user interaction and can be exploited through various input points within the plugin's functionality.
The mitigation strategies for CVE-2021-24857 primarily focus on immediate plugin updates to version 1.7.2 or later, which addresses the improper input handling and deserialization practices. Organizations should also implement comprehensive input validation and sanitization measures, ensuring that all user-supplied data is properly validated before any processing occurs. Security hardening practices should include disabling unnecessary plugin functionality and regularly auditing installed plugins for known vulnerabilities. Additionally, implementing web application firewalls and monitoring for suspicious deserialization patterns can provide additional layers of protection. The vulnerability demonstrates the importance of following secure coding practices and the potential dangers of improper data handling in PHP applications, aligning with ATT&CK technique T1548.002 for privilege escalation through malicious code execution.