CVE-2021-21123Public exploitNetwork attack vector

File restriction bypass via spoofed save extension

Published Feb 9, 2021 · Updated Aug 3, 2024

Insufficient input validation in Google Chrome before 88.0.4324.96 allows remote attackers to bypass file restrictions via crafted HTML. The File System Access API's showSaveFilePicker path accepts crafted extension metadata that lets the Save As dialog label a shortcut as an image. Exploitation requires interaction with the crafted page and save dialog; on Windows, the saved file can be a disguised LNK shortcut.

CVSS severity6.5
Medium
EPSS probability10.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient input validation in Google Chrome before 88.0.4324.96 allows remote attackers to bypass file restrictions via crafted HTML. The File System Access API's showSaveFilePicker path accepts crafted extension metadata that lets the Save As dialog label a shortcut as an image. Exploitation requires interaction with the crafted page and save dialog; on Windows, the saved file can be a disguised LNK shortcut.

The record

CVE
CVE-2021-21123
Published
Feb 9, 2021
Updated
Aug 3, 2024
Vendor
Google Cloud
Product
Google Chrome
Classifications
CWE-20, T1036.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 9, 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 <88.0.4324.96

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Google Chromeversion=unspecified <88.0.4324.96

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1036.007Double File Extension

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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