CVE-2021-23253 in Opera Mini
Summary
by MITRE • 01/12/2021
Opera Mini for Android below 53.1 displays URL left-aligned in the address field. This allows a malicious attacker to craft a URL with a long domain name, e.g. www.safe.opera.com.attacker.com. With the URL being left-aligned, the user will only see the front part (e.g. www.safe.opera.com…) The exact amount depends on the phone screen size but the attacker can craft a number of different domains and target different phones. Starting with version 53.1 Opera Mini displays long URLs with the top-level domain label aligned to the right of the address field which mitigates the issue.
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Analysis
by VulDB Data Team • 02/11/2021
This vulnerability represents a sophisticated phishing attack vector that exploits user trust in web browsers through deceptive URL presentation techniques. The flaw exists in Opera Mini for Android versions prior to 53.1 where the address bar displays URLs with left-aligned domain names, creating a scenario where attackers can craft malicious URLs that appear legitimate to users. The vulnerability stems from the browser's rendering behavior where long domain names are truncated at the end rather than the beginning, allowing attackers to append malicious subdomains that remain hidden from view. This design choice creates a deceptive environment where users may believe they are visiting a trusted website while actually navigating to a malicious domain that shares the same top-level domain but includes additional malicious subdomains. The issue demonstrates a fundamental flaw in user interface security design that directly impacts user trust and security awareness.
The technical implementation of this vulnerability involves the browser's address bar rendering algorithm that prioritizes left alignment over truncation strategy. When a URL exceeds the visible address bar capacity, the system truncates the domain name from the right side while maintaining left alignment, which means that attackers can strategically place their malicious domains within the visible portion of the URL. This allows for various attack vectors including homograph attacks, where attackers use similar looking characters to mimic legitimate domains, and domain hijacking where attackers use subdomain structures to appear as legitimate websites. The vulnerability specifically affects mobile browser environments where screen real estate is limited and the truncation behavior becomes more pronounced. The exact truncation behavior depends on screen dimensions and font rendering, making the attack surface adaptable across different device configurations.
The operational impact of this vulnerability extends beyond simple phishing attacks to encompass broader security implications for mobile browsing environments. Users may unknowingly navigate to malicious domains while believing they are visiting legitimate websites, creating a significant risk for credential theft, malware distribution, and financial fraud. The attack requires minimal technical expertise from threat actors who can simply construct URLs with malicious subdomains that appear legitimate when truncated. This vulnerability particularly affects users who rely on Opera Mini for Android in environments where they may be less security-aware or where mobile browsing security is not prioritized. The risk is compounded by the fact that many users do not verify the complete URL before interacting with web pages, especially when the interface appears trustworthy. This type of vulnerability directly relates to attack techniques described in the attack pattern taxonomy under the category of deception and social engineering.
The mitigation implemented in Opera Mini version 53.1 addresses the core issue by changing the URL display behavior to right-align the top-level domain component, ensuring that the most critical part of the domain name remains visible to users. This change aligns with security best practices for user interface design and follows the principle of least privilege in information display, where users should always see the most relevant security information. The fix demonstrates a proper response to the vulnerability by modifying the presentation layer rather than attempting to address the underlying trust model. This approach reduces the attack surface by making malicious domains more visible to users, thereby improving their ability to make informed decisions about website legitimacy. The solution also reflects industry standards for secure user interface design and aligns with the concept of security by design principles. The remediation approach is consistent with the recommendations found in various security frameworks that emphasize the importance of transparent and clear security indicators in user interfaces. This vulnerability and its resolution highlight the critical importance of considering security implications in all aspects of user interface design, particularly in mobile environments where screen constraints create additional attack vectors. The fix represents a defensive measure that directly addresses the specific security flaw without introducing additional complexity or performance impacts to the browser functionality.