CVE-2021-3968Public exploit

Editor crash via premature ModeChanged dispatch

Published Nov 19, 2021 · Updated Aug 3, 2024

Heap-based buffer overflow in Vim before 8.2.3610 allows context-dependent attackers to crash the editor via ModeChanged. The n_start_visual_mode function triggers ModeChanged before completing Visual-mode state setup, allowing a recursive autocommand to use inconsistent heap-backed editor state. Exploitation requires a ModeChanged autocommand to run during entry into Visual mode; the upstream regression test demonstrates an editor-process crash.

CVSS severity8.0
High
EPSS probability2.23%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in Vim before 8.2.3610 allows context-dependent attackers to crash the editor via ModeChanged. The n_start_visual_mode function triggers ModeChanged before completing Visual-mode state setup, allowing a recursive autocommand to use inconsistent heap-backed editor state. Exploitation requires a ModeChanged autocommand to run during entry into Visual mode; the upstream regression test demonstrates an editor-process crash.

The record

CVE
CVE-2021-3968
Published
Nov 19, 2021
Updated
Aug 3, 2024
Vendor
Vim
Product
Vim
Classifications
CWE-787, CWE-122
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Nov 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <8.2.3610

What conditions does exploitation require?

Attack vectorlocal
Required privilegesUnavailable in this record.

What is affected?

Vim · Vimversion=unspecified <8.2.3610

Published CVSS scores

8.0huntr.devCVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
8.0NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-122Heap-based Buffer Overflow

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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