CVE-2019-18624 in Opera Mini
Summary
by MITRE
Opera Mini for Android allows attackers to bypass intended restrictions on .apk file download/installation via an RTLO (aka Right to Left Override) approach, as demonstrated by misinterpretation of malicious%E2%80%AEtxt.apk as maliciouskpa.txt. This affects 44.1.2254.142553, 44.1.2254.142659, and 44.1.2254.143214.
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Analysis
by VulDB Data Team • 01/29/2024
This vulnerability in Opera Mini for Android represents a sophisticated input validation flaw that exploits Unicode bidirectional algorithm manipulations to circumvent security controls. The issue stems from the browser's improper handling of right-to-left override characters within filenames, specifically when processing .apk files that are intended to be restricted from automatic download or installation. The RTLO technique manipulates the visual representation of filenames by inserting Unicode control characters that cause the display to render the filename in reverse order, making malicious files appear as benign text files to users and automated security systems.
The technical implementation of this vulnerability leverages CWE-174, which describes the weakness of insufficient input sanitization in bidirectional text handling, combined with CWE-20, which addresses improper input validation. Attackers exploit this by crafting filenames that contain right-to-left override sequences, such as encoding malicious.txt.apk as malicious%E2%80%AEtxt.apk where the %E2%80%AE represents the Unicode right-to-left override character. When Opera Mini processes these filenames, it fails to properly validate the actual file extension, instead relying on the visually manipulated representation that appears as a legitimate text file.
This vulnerability has significant operational impact within mobile security contexts, particularly in enterprise environments where mobile device management systems rely on browser-based security controls. The attack vector demonstrates a clear path for privilege escalation through social engineering, as users may inadvertently download and install malicious applications believing them to be harmless text files. The affected versions 44.1.2254.142553, 44.1.2254.142659, and 44.1.2254.143214 represent a specific release series that failed to implement proper filename validation mechanisms. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 (Command and Scripting Interpreter: PowerShell) and T1190 (Exploit Public-Facing Application) through the manipulation of file type detection mechanisms.
The security implications extend beyond simple file type confusion, as this vulnerability could enable attackers to bypass application whitelisting policies and mobile security controls that rely on filename extensions for access control decisions. Organizations utilizing Opera Mini for Android in corporate environments face potential exposure to mobile malware distribution, as the browser's failure to properly validate file extensions creates a persistent attack surface. The vulnerability particularly affects environments with strict mobile device policies where automatic installation of application packages is restricted, as the RTLO attack can effectively neutralize these protections through visual deception.
Mitigation strategies should include immediate patching of affected Opera Mini versions, implementation of additional filename validation at the network level, and deployment of mobile security solutions that can detect and block RTLO character sequences in downloaded files. Network-based solutions should monitor for suspicious Unicode character patterns in file names and implement additional validation layers beyond simple file extension checks. Users should be educated about the visual deception techniques involved in RTLO attacks, and organizations should consider implementing application control policies that prevent automatic installation of applications from untrusted sources. The vulnerability also highlights the need for comprehensive Unicode handling in security controls, as demonstrated by the ATT&CK technique T1211 (Exploitation for Defense Evasion) which specifically addresses the use of character encoding manipulation for bypassing security controls.