CVE-2021-3875 in Vim
Summary
by MITRE • 10/15/2021
vim is vulnerable to Heap-based Buffer Overflow
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Analysis
by VulDB Data Team • 05/03/2025
The vulnerability identified as CVE-2021-3875 represents a critical heap-based buffer overflow flaw within the vim text editor software. This vulnerability exists in the handling of certain input data structures during the processing of specific file formats or commands within the vim environment. The flaw manifests when the application attempts to allocate memory on the heap for processing user-supplied data without adequate bounds checking, creating an exploitable condition that could allow malicious actors to manipulate memory allocation patterns. The vulnerability impacts various versions of vim across different operating systems and deployment scenarios where the editor is used to process untrusted input files or commands. Security researchers have identified that the buffer overflow occurs during the parsing of specific data structures, particularly when handling malformed input that triggers memory allocation routines beyond intended boundaries. This type of vulnerability falls under the CWE-122 category, which specifically addresses heap-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent heap memory locations. The vulnerability is particularly concerning because it can be exploited through carefully crafted input files that when opened or processed by vim, trigger the overflow condition. Attackers can leverage this weakness to execute arbitrary code within the context of the vim process, potentially leading to full system compromise. The exploitability of this vulnerability depends on several factors including the specific version of vim in use, the operating system environment, and the presence of security mitigations such as address space layout randomization and stack canaries. The operational impact of CVE-2021-3875 extends beyond simple code execution as it can also facilitate privilege escalation attacks, especially when vim is run with elevated privileges or in environments where users have the ability to process untrusted files. The vulnerability is particularly dangerous in server environments where vim might be used for processing user-uploaded content or in development environments where developers regularly open potentially malicious files. The memory corruption resulting from this heap overflow can be leveraged to overwrite critical data structures, function pointers, or return addresses, enabling attackers to redirect program execution flow. This vulnerability aligns with ATT&CK technique T1059 which covers command and scripting interpreter usage, as exploitation often involves crafting malicious input to trigger the vulnerable code path. Organizations using vim in production environments should consider the potential for remote code execution and privilege escalation when assessing risk. The vulnerability demonstrates the importance of proper input validation and memory management practices in text processing applications, as even seemingly benign operations like file viewing can become attack vectors. Security teams should prioritize patching affected systems and implementing additional monitoring for suspicious vim usage patterns that might indicate exploitation attempts. The presence of this vulnerability in widely-used text editors underscores the critical need for comprehensive security testing of core system utilities and the importance of maintaining up-to-date software versions across all infrastructure components. Organizations should also consider implementing application whitelisting policies to restrict vim usage to trusted environments and ensure that all users have appropriate security training regarding handling untrusted files. The exploitation of heap-based buffer overflows like CVE-2021-3875 represents a fundamental weakness in memory safety that affects numerous software applications beyond vim, making proper input validation and secure coding practices essential for preventing similar vulnerabilities in other software components.