CVE-2021-33898 in Invoice Ninja
Summary
by MITRE • 06/07/2021
In Invoice Ninja before 4.4.0, there is an unsafe call to unserialize() in app/Ninja/Repositories/AccountRepository.php that may allow an attacker to deserialize arbitrary PHP classes. In certain contexts, this can result in remote code execution. The attacker's input must be hosted at http://www.geoplugin.net (cleartext HTTP), and thus a successful attack requires spoofing that site or obtaining control of it.
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Analysis
by VulDB Data Team • 06/10/2021
The vulnerability identified as CVE-2021-33898 represents a critical security flaw in Invoice Ninja versions prior to 4.4.0, where an unsafe deserialization primitive exists within the application's codebase. This vulnerability resides in the app/Ninja/Repositories/AccountRepository.php file and specifically involves an unguarded call to PHP's unserialize() function. The flaw stems from the application's failure to properly validate or sanitize user input before passing it to the deserialization mechanism, creating a potential attack vector that could be exploited by malicious actors.
The technical nature of this vulnerability aligns with CWE-502, which categorizes unsafe deserialization as a dangerous practice that can lead to remote code execution when attacker-controlled data is processed through PHP's unserialize() function. The vulnerability operates under the assumption that an attacker can manipulate input data that eventually reaches the unserialize() call, allowing them to construct malicious serialized objects that, when deserialized, can execute arbitrary code on the target system. This type of vulnerability is particularly dangerous because it can bypass traditional input validation mechanisms and directly manipulate the application's object graph during runtime.
The operational impact of this vulnerability is significant, as it can potentially allow remote code execution when combined with the specific requirement for attacker-controlled data to be hosted at the geoplugin.net domain. This constraint creates a unique attack scenario where an attacker must either compromise the geoplugin.net domain or implement a man-in-the-middle attack to spoof the domain's responses. The attack requires the attacker to host malicious serialized data at the specific domain, making it somewhat more difficult to exploit compared to vulnerabilities that accept arbitrary input directly from users. However, the potential for remote code execution remains high, as successful exploitation can grant full control over the affected system.
The attack vector for this vulnerability requires an attacker to first gain control over the geoplugin.net domain or implement a DNS spoofing or HTTP interception attack to redirect traffic to their malicious infrastructure. Once the attacker has control over the domain, they can craft serialized PHP objects that, when processed by the vulnerable Invoice Ninja application, will execute arbitrary code on the server. This approach aligns with ATT&CK technique T1059.007, which involves the execution of code through PHP deserialization attacks. The requirement for cleartext HTTP communication and the specific domain targeting creates a unique operational context that differentiates this vulnerability from typical deserialization attacks.
Mitigation strategies for CVE-2021-33898 should prioritize immediate patching to version 4.4.0 or later, which addresses the unsafe unserialize() call through proper input validation and sanitization. Organizations should also implement network-level controls to prevent communication with the geoplugin.net domain unless absolutely necessary, and consider implementing DNS filtering and HTTP interception monitoring to detect potential attacks. Security teams should also conduct thorough code reviews to identify similar patterns of unsafe deserialization throughout the application codebase, as this vulnerability demonstrates how a single unsafe call can create a critical security risk. Additionally, organizations should implement proper input validation and sanitization practices, ensuring that any data passed to PHP's unserialize() function is properly authenticated and validated before processing to prevent similar vulnerabilities from being introduced in the future.