CVE-2020-15654
Published: April 11, 2026
Official 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.
Risk Analysis
This vulnerability in Firefox and Thunderbird allows a malicious website to manipulate the custom cursor, making it appear as if the user is interacting with the interface when they are not. While not directly leading to code execution, it can create a perceived broken state and potentially aid in phishing attempts.
This vulnerability has been actively exploited in the wild and is listed in CISA's KEV catalog. Attackers are using this flaw to create deceptive user experiences.
Update Firefox to version 79 or later, Firefox ESR to 78.1 or later, and Thunderbird to 78.1 or later. Users should also be cautious of suspicious websites and unexpected browser behavior.
Technical Analysis
CVE-2020-15654 requires local access, meaning attackers must already have a foothold on the target system.
Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.
CISA has added CVE-2020-15654 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.
Exploit & PoC Resources
Quick Facts
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2020-15654 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts
- !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
- !Active exploitation confirmed — treat as P1