What’s Vulnerable › Vulnerabilities

CVE-2020-15654

• Severity: medium (CVSS 6.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-08-10 · updated 2026-06-17
• Weakness: CWE-835

Description

When in an endless loop, a website specifying a custom cursor using CSS could make it look like the user is interacting with the user interface, when they are not. This could lead to a perceived broken state, especially when interactions with existing browser dialogs and warnings do not work. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

Affected products

• Canonical Ubuntu Linux: 16.04, 18.04, 20.04
• Mozilla Firefox: before 79.0 — fixed in 79.0
• Mozilla Firefox ESR: before 78.1 — fixed in 78.1
• Mozilla Thunderbird: before 78.1 — fixed in 78.1

How to fix

Upgrade to a fixed version: Mozilla Firefox 79.0; Mozilla Firefox ESR 78.1; Mozilla Thunderbird 78.1. Check the vendor advisory for mitigations.

References

• http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00025.html
• https://bugzilla.mozilla.org/show_bug.cgi?id=1648333
• https://usn.ubuntu.com/4443-1/
• https://www.mozilla.org/security/advisories/mfsa2020-30/
• https://www.mozilla.org/security/advisories/mfsa2020-32/
• https://www.mozilla.org/security/advisories/mfsa2020-33/
• http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00025.html
• https://bugzilla.mozilla.org/show_bug.cgi?id=1648333
• https://usn.ubuntu.com/4443-1/
• https://www.mozilla.org/security/advisories/mfsa2020-30/
• https://www.mozilla.org/security/advisories/mfsa2020-32/
• https://www.mozilla.org/security/advisories/mfsa2020-33/

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