CVE-2017-7791 in Firefox
Summary
by MITRE
On pages containing an iframe, the "data:" protocol can be used to create a modal alert that will render over arbitrary domains following page navigation, spoofing of the origin of the modal alert from the iframe content. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a sophisticated cross-origin information disclosure and user interface spoofing flaw that exploits the handling of data protocol URLs within iframe contexts. The issue stems from how web browsers process data: URLs that contain embedded content directly within the URL itself, allowing for the creation of modal dialogs without proper origin validation. When an iframe loads content using a data: protocol URL, the browser renders this content in a way that bypasses normal security boundaries, enabling malicious actors to create deceptive alerts that appear to originate from the parent page's domain rather than the iframe's actual source.
The technical implementation of this vulnerability involves the manipulation of iframe content through data: protocol URLs which can contain HTML and JavaScript code directly within the URL structure. This creates a scenario where navigation events trigger modal dialog displays that render over the entire page, effectively overlaying the user interface with content that can masquerade as legitimate interface elements from trusted domains. The flaw specifically affects browsers that fail to properly validate the origin of modal dialogs created through data: protocol content, allowing attackers to craft deceptive user interfaces that can trick users into believing they are interacting with legitimate applications.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass user deception and potential phishing attacks. Attackers can leverage this flaw to create convincing fake authentication dialogs, security warnings, or application interfaces that appear to originate from trusted domains, potentially leading users to unknowingly provide sensitive information or perform actions they would not otherwise take. This type of vulnerability aligns with attack patterns documented in the attack tree framework where adversaries exploit browser security boundaries to establish deception environments. The vulnerability affects a broad range of browser versions including Thunderbird and various Firefox releases, indicating a widespread impact across multiple software ecosystems.
Security researchers categorize this vulnerability under CWE-601 as an open redirect vulnerability that enables URL spoofing, while also demonstrating characteristics of CWE-79 which addresses cross-site scripting flaws. The ATT&CK framework would classify this under T1059 for execution through script-based attacks and T1566 for social engineering techniques that exploit user trust in familiar interfaces. The vulnerability's exploitation requires minimal user interaction beyond navigation, making it particularly dangerous as it can be triggered automatically during page load or user navigation events. Organizations should implement immediate mitigations including browser updates to patched versions, implementation of content security policies, and user education regarding suspicious interface elements that appear unexpectedly during page navigation.
The remediation approach for this vulnerability centers on browser vendor patches that enforce stricter validation of modal dialog origins and proper handling of data: protocol URLs within iframe contexts. Security teams should monitor for any attempts to exploit this vulnerability through malicious iframe content and implement proactive measures such as CSP headers that restrict data: protocol usage and prevent unauthorized modal dialog creation. Additionally, this vulnerability highlights the importance of maintaining up-to-date browser software and implementing comprehensive security monitoring to detect potential exploitation attempts. The fix typically involves modifying browser rendering engines to ensure that modal dialogs created through data: protocol content cannot spoof the origin of the parent page, requiring careful attention to how browser security boundaries are enforced during page navigation events.