CVE-2023-4581Public exploitNetwork attack vector

Malicious XLL delivery via missing executable-blocklist entry

Published Sep 11, 2023 · Updated Dec 18, 2025

Protection-mechanism failure in Mozilla Firefox, Firefox ESR, and Thunderbird allows remote attackers to deliver .xll files without warnings. The executable-file blocklist omitted its Windows-specific xll entry, so the download handler treated the add-in like an ordinary file. A user must download and open the file in Microsoft Excel; that interaction can load attacker-supplied native code through the add-in.

CVSS severity4.3
Medium
EPSS probability0.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Protection-mechanism failure in Mozilla Firefox, Firefox ESR, and Thunderbird allows remote attackers to deliver .xll files without warnings. The executable-file blocklist omitted its Windows-specific xll entry, so the download handler treated the add-in like an ordinary file. A user must download and open the file in Microsoft Excel; that interaction can load attacker-supplied native code through the add-in.

The record

CVE
CVE-2023-4581
Published
Sep 11, 2023
Updated
Dec 18, 2025
Vendor
Mozilla
Product
Firefox
Classifications
T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 11, 2023CVE publishedPublication date reported by the CVE source.
  2. Dec 18, 2025Record 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 <117

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <117
Mozilla · Thunderbirdversion=unspecified <102.15; version=unspecified <115.2
Mozilla · Firefox ESRversion=unspecified <102.15; version=unspecified <115.2

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/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

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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