CVE-2021-40836 in Antivirus Engine
Summary
by MITRE • 12/22/2021
A vulnerability affecting F-Secure antivirus engine was discovered whereby scanning MS outlook .pst files can lead to denial-of-service. The vulnerability can be exploited remotely by an attacker. A successful attack will result in denial-of-service of the antivirus engine.
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Analysis
by VulDB Data Team • 12/25/2021
The vulnerability identified as CVE-2021-40836 represents a significant security flaw within the F-Secure antivirus engine that specifically targets Microsoft Outlook .pst file processing capabilities. This weakness manifests during the routine scanning operations performed by the antivirus software when encountering .pst files, which are essential components of Microsoft Outlook email client storing user emails, contacts, and calendar information. The vulnerability operates at the intersection of email archiving systems and antivirus protection mechanisms, creating a potential attack surface that could be exploited by malicious actors seeking to disrupt legitimate security operations.
The technical nature of this flaw stems from improper handling of malformed or specially crafted .pst file structures during the antivirus scanning process. When the F-Secure engine attempts to parse and analyze these email archive files, it fails to adequately validate input data, leading to unexpected behavior that ultimately results in system instability. This type of vulnerability typically falls under CWE-129 Input Validation, where insufficient validation of input parameters leads to system resource exhaustion or memory corruption. The flaw demonstrates a classic case of inadequate error handling within the antivirus engine's file parsing routines, particularly when processing complex binary formats like .pst files that contain nested structures and metadata that require careful interpretation.
The operational impact of this vulnerability extends beyond simple service disruption, as it creates a remote attack vector that allows adversaries to target systems running F-Secure antivirus software without requiring physical access or elevated privileges. An attacker could potentially craft malicious .pst files designed to trigger the specific code path that leads to denial-of-service conditions, thereby compromising the availability of security services on targeted systems. This represents a critical weakness in the security infrastructure since antivirus engines are fundamental components of endpoint protection, and their compromise directly affects an organization's ability to detect and prevent other security threats. The vulnerability aligns with ATT&CK technique T1499.004, specifically targeting the availability of services through resource exhaustion or system instability.
From a defensive perspective, organizations utilizing F-Secure antivirus solutions must implement immediate mitigation strategies to protect against potential exploitation of this vulnerability. The primary recommendation involves applying the latest security patches provided by F-Secure, as these updates typically contain fixed implementations of the vulnerable code paths. Additionally, network administrators should consider implementing additional monitoring and alerting mechanisms to detect unusual scanning behavior or system performance degradation that might indicate exploitation attempts. The vulnerability also highlights the importance of maintaining up-to-date antivirus signatures and ensuring that endpoint protection solutions are regularly updated to address newly discovered threats. Organizations should also consider implementing file access controls and quarantine procedures for .pst files, particularly those received from external sources, to minimize exposure to potentially malicious content. Security teams should conduct regular vulnerability assessments to identify similar weaknesses in other security tools and ensure comprehensive protection across their entire security infrastructure.