CVE-2021-3984Public exploit

Editor crash via stale C-indentation cursor column

Published Dec 1, 2021 · Updated Aug 3, 2024

Heap-based buffer overflow in Vim before 8.2.3625 allows context-dependent attackers to crash the editor via crafted C text. The find_start_brace function updates only the cursor line after locating a brace, leaving a stale column that makes C-indentation inspect beyond the new line's end. Exploitation requires a user to process and reindent the crafted content, and the demonstrated consequence is an editor crash.

CVSS severity7.8
High
EPSS probability1.46%
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 8.2.3625 allows context-dependent attackers to crash the editor via crafted C text. The find_start_brace function updates only the cursor line after locating a brace, leaving a stale column that makes C-indentation inspect beyond the new line's end. Exploitation requires a user to process and reindent the crafted content, and the demonstrated consequence is an editor crash.

The record

CVE
CVE-2021-3984
Published
Dec 1, 2021
Updated
Aug 3, 2024
Vendor
Vim
Product
Vim
Classifications
CWE-122, CWE-787, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 1, 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 <8.2.3625

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Vim · Vimversion=unspecified <8.2.3625

Published CVSS scores

7.3huntr.devCVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:H/A:H
6.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:P
7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-122Heap-based Buffer Overflow
CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

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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