CVE-2026-87599 in Chrome
Summary
by MITRE • 09/09/2026
Improper input validation in Interstitials in Google Chrome prior to 153.0.8010.36 allowed a remote attacker to spoof UI elements via a crafted HTML page. (Chromium security severity: Medium)
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified as an improper input validation flaw within the interstitial handling mechanisms of Google Chrome prior to version 153.0.8010.36 represents a significant risk related to user interface spoofing and trust boundary violations. Interstitials in web browsers are typically used to display important messages such as certificate errors, security warnings, or navigation confirmations before allowing the user to proceed with their intended action. These elements are designed to be distinct from standard webpage content to ensure that users can clearly distinguish between browser-generated UI and third-party website content. The flaw arises when the browser fails to adequately sanitize or validate input data associated with these interstitial displays, potentially allowing malicious actors to inject crafted HTML structures that mimic legitimate browser interfaces. This specific weakness is categorized under CWE-20 Improper Input Validation, which encompasses scenarios where software receives external input and does not verify its correctness before processing it.
The operational impact of this vulnerability centers on the potential for user interface spoofing, a technique often associated with social engineering attacks. By crafting an HTML page that exploits the validation gap in interstitial handling, a remote attacker can create deceptive overlays or pop-ups that appear to originate from Chrome itself rather than the visited website. These fake UI elements could mimic common browser warnings such as phishing alerts, certificate invalidity notices, or download confirmation dialogs. The primary consequence is the erosion of user trust and awareness. Users who are accustomed to relying on these specific visual cues for security decisions may be misled into believing that a malicious site is safe or that a dangerous action is authorized by their browser. This can lead users to inadvertently proceed with navigating to phishing sites, downloading malware-laden files, or submitting sensitive credentials to fraudulent login pages disguised as legitimate services.
From an offensive security perspective, this vulnerability aligns closely with the MITRE ATT&CK technique of Masquerading (T1036), where attackers disguise their actions to appear like something else. Specifically, it relates to sub-techniques involving UI redressing or spoofing trusted interfaces. The ability to inject content that mimics browser chrome allows an attacker to bypass user vigilance mechanisms that rely on visual differentiation between application frames and web page content. This is particularly dangerous in contexts where users are already under pressure or distraction, as the forged interstitial may appear authoritative due to its resemblance to standard Chrome security dialogs. The severity of this issue is classified as Medium within the Chromium security framework, reflecting the fact that while it does not directly allow for arbitrary code execution or sandbox escape, it significantly compromises the integrity of the user's decision-making process regarding web navigation and data submission.
Mitigation strategies primarily involve updating to a patched version of Google Chrome where these input validation checks have been strengthened. For organizations managing large fleets of browsers, deploying automated patch management solutions is critical to ensure that all endpoints are updated past version 153.0.8010.36 promptly. Additionally, security awareness training should emphasize the importance of verifying URL bars and certificate details even when interstitials appear, as sophisticated attackers may attempt to manipulate these elements further. Users can also enable features such as Safe Browsing or enhanced phishing protection which add additional layers of verification beyond simple UI cues. From a development standpoint, this incident highlights the necessity for rigorous input sanitization in all components that interact with user-facing interfaces, ensuring that any dynamic content injected into interstitials is strictly validated against expected formats and origins to prevent injection attacks.