CVE-2021-3928 in Vim
Summary
by MITRE • 11/05/2021
vim is vulnerable to Stack-based Buffer Overflow
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Analysis
by VulDB Data Team • 11/10/2021
The vulnerability identified as CVE-2021-3928 represents a critical stack-based buffer overflow flaw within the vim text editor software. This vulnerability stems from improper input validation and memory management practices during the processing of specific file formats, particularly affecting how vim handles certain escape sequences and control characters within text files. The flaw exists in the editor's parsing mechanism that fails to properly bounds-check data when reading and processing file content, creating opportunities for malicious actors to exploit the vulnerability through crafted input files.
The technical implementation of this buffer overflow occurs when vim processes files containing specially constructed sequences that exceed the allocated stack buffer size. The vulnerability manifests during the rendering or processing of text content where the software attempts to store data beyond the boundaries of a pre-allocated memory buffer on the stack. This flaw can be triggered when vim encounters malformed escape sequences or control character combinations that cause the program to write beyond the intended memory allocation, potentially overwriting adjacent stack memory locations including return addresses and function pointers.
From an operational perspective, this vulnerability presents significant security risks to systems where vim is used for editing files from untrusted sources. Attackers can exploit this flaw by crafting malicious files that, when opened in vim, trigger the buffer overflow condition. The exploitation can lead to arbitrary code execution, denial of service conditions, or privilege escalation depending on the target system configuration and execution context. The vulnerability affects various versions of vim across different operating systems, making it a widespread concern for organizations relying on this popular text editing tool. Security researchers have noted that the exploitability of this vulnerability increases when vim is used in automated environments or when users frequently open files from external sources without proper validation.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflow conditions occurring in stack memory regions. This classification indicates that the flaw involves insufficient boundary checking in stack-allocated buffers, making it susceptible to overwrite critical program execution data. From an attack framework perspective, this vulnerability can be mapped to multiple ATT&CK techniques including T1059 Command and Scripting Interpreter and T1203 Exploitation for Client Execution, as it enables adversaries to execute malicious code through compromised text editor processes. The attack surface is particularly broad given vim's prevalence across Unix-like systems, Linux distributions, and Windows environments where it may be installed as part of development toolchains or system administration utilities.
Mitigation strategies for CVE-2021-3928 primarily involve applying the latest security patches and updates provided by vim maintainers and operating system vendors. System administrators should prioritize updating vim installations to versions that include memory bounds checking improvements and input validation fixes. Additional protective measures include implementing file access controls that restrict vim's ability to process untrusted files, using sandboxing techniques to contain potential exploitation attempts, and deploying intrusion detection systems that can identify suspicious file access patterns. Organizations should also consider implementing automated scanning tools that can detect and prevent the opening of potentially malicious files through vim, particularly in environments where users regularly handle files from external sources. Regular security assessments of text editor configurations and user access controls can further reduce the attack surface and minimize the risk of successful exploitation attempts.