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High severity7.8NVD Advisory· Published Dec 1, 2021· Updated May 29, 2026

CVE-2021-4019

CVE-2021-4019

Description

A heap-based buffer overflow in vim's help tag processing allows arbitrary code execution when opening a crafted help file.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A heap-based buffer overflow in vim's help tag processing allows arbitrary code execution when opening a crafted help file.

Vulnerability

A heap-based buffer overflow exists in the find_help_tags function of vim (before patch 8.2.3669). When processing a long help argument, the unsafe use of STRCPY without bounds checking can overflow a heap buffer. This occurs in the code path that handles help tags with a leading % or _ character [1][2].

Exploitation

An attacker can exploit this vulnerability by convincing a user to open a specially crafted help file or to execute the :help command with an overly long argument. No authentication is required, but user interaction is necessary. The attacker must provide a string longer than the allocated buffer (e.g., a help argument of 1021 characters as shown in the test case) [2].

Impact

Successful exploitation leads to a heap-based buffer overflow, which can corrupt adjacent memory. This may allow an attacker to execute arbitrary code with the privileges of the user running vim, or cause a denial of service via a crash. The impact is limited to the user's session and does not cross privilege boundaries unless vim is running with elevated privileges [1].

Mitigation

The vulnerability is fixed in vim version 8.2.3669, released on 2021-09-30 (commit bd228fd097b41a798f90944b5d1245eddd484142) [2]. Users should update to this or a later version. No workaround is available. The CVE is not listed in the CISA Known Exploited Vulnerabilities catalog.

References
  1. security - Re: 3 new CVE's in vim
  2. patch 8.2.3669: buffer overflow with long help argument · vim/vim@bd228fd

AI Insight generated on May 29, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

44

Patches

0

No patches discovered yet.

Vulnerability mechanics

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References

9

News mentions

0

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