CVE-2020-9331 in CSP
Summary
by MITRE • 10/23/2020
CryptoPro CSP through 5.0.0.10004 on 32-bit platforms allows Local Privilege Escalation (by local users with the SeChangeNotifyPrivilege right) because user-mode input is mishandled during process creation. An attacker can write arbitrary data to an arbitrary location in the kernel's address space.
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Analysis
by VulDB Data Team • 11/27/2020
The vulnerability identified as CVE-2020-9331 represents a critical local privilege escalation flaw within the CryptoPro Cryptographic Service Provider implementation on 32-bit Windows systems. This vulnerability affects versions up to and including 5.0.0.10004, creating a significant security risk for systems that utilize this cryptographic service provider. The flaw specifically targets the process creation mechanism within the user-mode component of the cryptographic service provider, where input validation and handling procedures have been found to be insufficient. The vulnerability is particularly dangerous because it allows an attacker with the SeChangeNotifyPrivilege right to manipulate kernel memory directly, effectively bypassing standard operating system security boundaries.
The technical root cause of this vulnerability stems from improper validation of user-mode input during the process creation sequence within the CryptoPro CSP module. When a process is initiated through the cryptographic service provider, the system fails to properly sanitize or validate the input parameters that are passed to kernel-level functions. This inadequate input handling creates a path where maliciously crafted data can be written to arbitrary memory locations within the kernel address space. The vulnerability operates at the intersection of user-mode and kernel-mode execution contexts, where the cryptographic service provider's process creation routine does not adequately protect against malicious input that could be manipulated to overwrite kernel memory. This flaw is classified under CWE-121 as a stack-based buffer overflow, though it manifests more specifically as a kernel memory corruption vulnerability due to the direct kernel address space manipulation capability.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to gain complete control over the affected system's kernel memory space. An attacker with the SeChangeNotifyPrivilege right can leverage this vulnerability to execute arbitrary code in kernel context, effectively bypassing all standard user-mode security controls including application whitelisting, user access controls, and process isolation mechanisms. The ability to write arbitrary data to kernel memory locations means that an attacker can modify critical system structures, replace kernel functions, or manipulate system call tables to maintain persistence and further escalate privileges. This vulnerability essentially creates a backdoor for kernel-level attacks, allowing for complete system compromise without requiring elevated privileges initially, and can be exploited to install rootkits, modify system binaries, or disable security features. The impact is particularly severe on 32-bit systems where kernel memory layout is more predictable and vulnerable to such attacks.
Mitigation strategies for CVE-2020-9331 must address both the immediate vulnerability and the broader security posture of systems running affected CryptoPro CSP versions. The primary recommendation involves applying the vendor-provided security patches and updates that address the specific input validation flaws in the process creation mechanism. Organizations should also implement strict privilege controls to limit which users possess the SeChangeNotifyPrivilege right, as this privilege is essential for exploitation of the vulnerability. Network segmentation and system hardening measures should be implemented to reduce the attack surface, including disabling unnecessary services and restricting access to systems running the vulnerable cryptographic service provider. Additionally, monitoring for suspicious process creation patterns and anomalous memory access behaviors can help detect exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and kernel-mode exploitation methods, specifically targeting the T1068 privilege escalation tactic and T1547.001 registry run keys or T1547.009 service creation techniques that could be used to maintain persistence after exploitation. Organizations should also consider implementing kernel-mode protection mechanisms such as kernel patch protection and driver signature enforcement to prevent exploitation of similar vulnerabilities in the future.