CVE-2017-5415 in Firefox
Summary
by MITRE
An attack can use a blob URL and script to spoof an arbitrary addressbar URL prefaced by "blob:" as the protocol, leading to user confusion and further spoofing attacks. This vulnerability affects Firefox < 52.
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Analysis
by VulDB Data Team • 06/22/2025
This vulnerability represents a sophisticated browser-based deception mechanism that exploits the handling of blob URLs in Firefox versions prior to 52. The flaw allows attackers to manipulate the browser's address bar display through the use of blob URLs, which are temporary identifiers for binary data stored in memory rather than on disk. When a malicious script creates a blob URL and navigates the browser to it, the address bar can be manipulated to display a spoofed URL that appears to originate from a trusted source but is actually prefixed with the blob: protocol. This creates a deceptive user experience where the browser interface misleadingly indicates the source of content, potentially leading users to believe they are visiting a legitimate website when they are actually viewing malicious content.
The technical implementation of this vulnerability stems from Firefox's insufficient validation of blob URL display in the address bar. When blob URLs are processed, the browser fails to properly sanitize or validate the displayed protocol information, allowing arbitrary content to be presented as if it were from a legitimate source. This issue specifically affects the rendering of the address bar where the URL is displayed, creating a mismatch between the actual content source and what the user perceives. The vulnerability operates at the intersection of web security boundaries, exploiting the trust users place in address bar information while bypassing normal security mechanisms that would otherwise prevent such spoofing attacks.
The operational impact of this vulnerability extends beyond simple user confusion to potentially enable more sophisticated phishing and social engineering attacks. Attackers can leverage this flaw to create convincing fake login pages, banking interfaces, or other trusted-looking web applications that appear to be legitimate sites. The blob: protocol prefix creates a deceptive visual cue that can bypass user security awareness and traditional phishing detection mechanisms. This vulnerability particularly affects users who rely on visual cues from the address bar to verify website authenticity, making it a significant threat vector for credential theft and other malicious activities. The attack requires minimal user interaction beyond visiting a malicious webpage, making it particularly dangerous in phishing campaigns.
Security professionals should consider this vulnerability in the context of the broader ATT&CK framework, specifically under the T1566 technique for Phishing and T1071 for Application Layer Protocol usage. The vulnerability aligns with CWE-601 Open Redirect vulnerabilities where users are redirected to malicious sites through deceptive means. Organizations should implement immediate mitigations including updating Firefox to version 52 or later, where the vulnerability has been patched through enhanced validation of blob URL display in the address bar. Additional defensive measures include user education about address bar verification, implementation of browser security extensions, and monitoring for suspicious URL patterns in network traffic. The patch for this vulnerability specifically addresses the validation of blob URL protocol handling and ensures that the address bar correctly represents the actual source of content rather than allowing arbitrary spoofing through blob URL manipulation.