CVE-2021-4166 in macOS
Summary
by MITRE • 12/26/2021
vim is vulnerable to Out-of-bounds Read
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Analysis
by VulDB Data Team • 10/21/2025
The vulnerability identified as CVE-2021-4166 affects the vim text editor, specifically exposing an out-of-bounds read condition that can be exploited by malicious actors. This issue arises from improper input validation within the editor's handling of certain file formats or commands, allowing attackers to access memory locations beyond the intended buffer boundaries. The vulnerability exists in the core parsing mechanisms that process various text files, particularly those with complex formatting or embedded special characters. An out-of-bounds read represents a critical security flaw that can potentially lead to information disclosure, application instability, or even remote code execution depending on the specific implementation details and system configuration.
The technical root cause of this vulnerability stems from inadequate bounds checking during the processing of input data within vim's internal memory management systems. When the editor encounters malformed or specially crafted input sequences, it fails to properly validate array indices or buffer limits before accessing memory locations. This flaw falls under the Common Weakness Enumeration category of CWE-129, which specifically addresses improper validation of array indices and buffer over-read conditions. The vulnerability manifests when vim attempts to parse text files containing specific patterns that trigger the out-of-bounds memory access, potentially exposing sensitive data from adjacent memory locations or causing unexpected program behavior.
The operational impact of CVE-2021-4166 extends beyond simple data corruption, as it creates potential attack vectors that can be leveraged by threat actors in various scenarios. In environments where vim is used to process untrusted input, such as web applications, automated systems, or collaborative editing platforms, this vulnerability can enable attackers to extract confidential information from memory segments. The risk is particularly elevated in server environments or automated workflows where vim processes files from external sources without proper sanitization. Additionally, the vulnerability can contribute to denial-of-service conditions that may disrupt legitimate user operations or system availability.
Mitigation strategies for this vulnerability should encompass multiple layers of protection to ensure comprehensive security coverage. System administrators should prioritize updating vim installations to versions that contain patches addressing the out-of-bounds read condition, following the vendor's security advisories and release notes. Implementing proper input validation and sanitization measures can help prevent exploitation attempts, while network segmentation and access controls can limit potential attack surfaces. The vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as attackers may leverage vim's functionality to execute malicious code through specially crafted input files. Organizations should also consider implementing runtime monitoring solutions that can detect anomalous memory access patterns and provide early warning of potential exploitation attempts. Regular security assessments and vulnerability scanning should include checks for this specific flaw to ensure timely remediation across all affected systems.