What’s Vulnerable › Vulnerabilities

CVE-2023-4581: XLL file extensions were downloadable without warnings

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-09-11 · updated 2026-06-17

Description

Excel `.xll` add-in files did not have a blocklist entry in Firefox's executable blocklist which allowed them to be downloaded without any warning of their potential harm. This vulnerability affects Firefox < 117, Firefox ESR < 102.15, Firefox ESR < 115.2, Thunderbird < 102.15, and Thunderbird < 115.2.

Affected products

• Mozilla Firefox: before 117.0; from 115.0 before 115.2 — fixed in 115.2, 117.0
• Mozilla Firefox ESR: before 102.15 — fixed in 102.15
• Mozilla Thunderbird: before 115.2 — fixed in 115.2

How to fix

Upgrade to a fixed version: Mozilla Firefox 115.2, 117.0; Mozilla Firefox ESR 102.15; Mozilla Thunderbird 115.2. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=1843758
• https://www.mozilla.org/security/advisories/mfsa2023-34/
• https://www.mozilla.org/security/advisories/mfsa2023-35/
• https://www.mozilla.org/security/advisories/mfsa2023-36/
• https://www.mozilla.org/security/advisories/mfsa2023-37/
• https://www.mozilla.org/security/advisories/mfsa2023-38/
• https://bugzilla.mozilla.org/show_bug.cgi?id=1843758
• https://www.mozilla.org/security/advisories/mfsa2023-34/
• https://www.mozilla.org/security/advisories/mfsa2023-35/
• https://www.mozilla.org/security/advisories/mfsa2023-36/
• https://www.mozilla.org/security/advisories/mfsa2023-37/
• https://www.mozilla.org/security/advisories/mfsa2023-38/

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