CVE-2021-23439Public exploitNetwork attack vector

Script execution via unescaped filename preview

Published Sep 5, 2021 · Updated Sep 16, 2024

Cross-site scripting in file-upload-with-preview before 4.2.0 allows remote attackers to execute script via a crafted filename. The single-file preview path assigns File.name directly to the upload control label's innerHTML, causing browser parsing instead of literal text display. Execution requires a user to select the attacker-supplied file, and the script runs in the context of the web page that embeds the library.

CVSS severity6.1
Medium
EPSS probability0.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in file-upload-with-preview before 4.2.0 allows remote attackers to execute script via a crafted filename. The single-file preview path assigns File.name directly to the upload control label's innerHTML, causing browser parsing instead of literal text display. Execution requires a user to select the attacker-supplied file, and the script runs in the context of the web page that embeds the library.

The record

CVE
CVE-2021-23439
Published
Sep 5, 2021
Updated
Sep 16, 2024
Vendor
John Datserakis
Product
file-upload-with-preview
Classifications
CWE-79, T1059.007, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 5, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 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 <4.2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

John Datserakis · file-upload-with-previewversion=unspecified <4.2.0

Published CVSS scores

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.2SnykCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007JavaScript
T1204.002Malicious File

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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