CVE-2026-0890 is a DOM-based spoofing vulnerability identified in Mozilla Firefox versions earlier than 147 and Firefox ESR versions earlier than 140.7. The vulnerability specifically affects the Copy & Paste and Drag & Drop components within the browser's Document Object Model (DOM) implementation. These components handle user interactions involving clipboard operations and drag-and-drop functionality, which are common in web applications and user workflows. The flaw allows an attacker to manipulate the data involved in these operations, potentially causing the browser to display or process spoofed content. This could mislead users into believing they are interacting with legitimate data or interfaces when in fact the content has been altered by an attacker. Such manipulation can lead to social engineering attacks, phishing, or unauthorized actions initiated by the user under false pretenses. The vulnerability does not require authentication or user privileges beyond normal browsing capabilities, and no user interaction beyond typical copy-paste or drag-and-drop actions is necessary. Although no exploits have been reported in the wild, the potential for misuse exists due to the widespread use of these browser features. The absence of a CVSS score limits precise severity quantification, but the risk centers on confidentiality and integrity impacts through user deception rather than direct system compromise or availability disruption.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of user interactions within web browsers. Attackers could exploit the spoofing flaw to trick employees into copying malicious content, pasting harmful data, or dragging and dropping spoofed elements, potentially leading to credential theft, unauthorized data disclosure, or execution of unintended commands. This could facilitate phishing campaigns, data leakage, or lateral movement within corporate networks if combined with other attack vectors. Organizations in sectors with high reliance on secure web communications, such as finance, government, and critical infrastructure, may face elevated risks. The impact is heightened in environments where Firefox is a standard browser and where users frequently engage in copy-paste or drag-and-drop operations with sensitive data. While no direct system compromise is indicated, the indirect effects on user trust and data integrity could lead to significant operational and reputational damage.

Organizations should prioritize updating Mozilla Firefox to version 147 or Firefox ESR 140.7 or later as soon as official patches become available. Until patches are applied, users should be educated about the risks of interacting with untrusted web content, especially involving copy-paste and drag-and-drop actions. Implementing browser security policies that restrict clipboard and drag-and-drop operations on untrusted sites can reduce exposure. Security teams should monitor for suspicious user behavior indicative of spoofing or social engineering attempts. Additionally, deploying endpoint security solutions capable of detecting anomalous clipboard or drag-and-drop activities may provide early warning. Regular audits of browser extensions and plugins should be conducted to ensure they do not exacerbate the vulnerability. Finally, integrating this vulnerability into organizational risk assessments and incident response plans will improve preparedness.