CVE-2021-3796 in Vim
Summary
by MITRE • 09/15/2021
vim is vulnerable to Use After Free
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Analysis
by VulDB Data Team • 05/03/2025
The vulnerability identified as CVE-2021-3796 represents a critical use after free condition within the vim text editor software. This flaw occurs when the application attempts to access memory that has already been freed, creating a potential avenue for arbitrary code execution. The vulnerability manifests during specific operations involving the handling of complex data structures within vim's memory management system, where improper memory deallocation followed by subsequent access creates exploitable conditions.
This use after free vulnerability falls under the common weakness enumeration CWE-416 which specifically addresses the use of freed memory condition. The flaw is particularly concerning as it can be exploited through carefully crafted input that triggers the problematic memory management sequence within vim's processing pipeline. Attackers can leverage this condition to execute malicious code with the privileges of the user running vim, potentially leading to complete system compromise. The vulnerability demonstrates poor memory management practices that violate fundamental security principles governing safe programming practices.
The operational impact of CVE-2021-3796 extends beyond simple privilege escalation as it can be weaponized in various attack scenarios. An attacker could craft malicious files or input that when processed by vim would trigger the use after free condition, allowing for remote code execution. This vulnerability affects systems where vim is installed and actively used, particularly in server environments where administrators may use vim for configuration file editing. The exploitability of this condition increases when vim is used in automated processes or when users open untrusted files without proper sanitization.
From an attack framework perspective, this vulnerability aligns with techniques described in the attack tactic of execution within the MITRE ATT&CK framework, where adversaries leverage software vulnerabilities to execute malicious code. The vulnerability can be exploited through multiple vectors including file-based attacks, network-based exploitation, or social engineering scenarios where users are tricked into opening malicious files within vim. Security professionals should consider this vulnerability as part of broader exploitation chains that may include privilege escalation, lateral movement, or persistence mechanisms.
Mitigation strategies for CVE-2021-3796 should prioritize immediate patching of affected vim installations, as the vulnerability exists in multiple versions of the software. Organizations should implement proper input validation and sanitization measures when processing files through vim, particularly in automated environments. The use of memory safety tools and static analysis should be employed to identify similar patterns in other software components. Additionally, system administrators should monitor for exploitation attempts and consider network segmentation to limit potential attack surfaces. Regular security updates and vulnerability management processes should be strengthened to prevent similar memory safety issues from occurring in other applications.