CVE-2015-5883 in Mac OS X
Summary
by MITRE
The bidirectional text-display and text-selection implementations in Terminal in Apple OS X before 10.11 interpret directional override formatting characters differently, which allows remote attackers to spoof the content of a text document via a crafted character sequence.
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Analysis
by VulDB Data Team • 11/21/2024
The vulnerability identified as CVE-2015-5883 resides within the Terminal application of Apple's macOS operating system, specifically affecting versions prior to 10.11. This issue manifests in the bidirectional text-display and text-selection mechanisms that handle complex text rendering for languages using right-to-left scripts such as Arabic and Hebrew. The flaw stems from the improper interpretation of directional override formatting characters that are part of the Unicode standard and are essential for correctly displaying mixed-directional text content. These characters include the left-to-right override (LRO), right-to-left override (RLO), left-to-right embedding (LRE), and right-to-left embedding (RLE) codes that are used to control text direction in multilingual environments.
The technical implementation of this vulnerability allows attackers to craft specific character sequences that exploit the inconsistent handling of these directional override codes between different text rendering contexts. When Terminal processes text containing these crafted sequences, it fails to properly normalize or sanitize the directional formatting characters, leading to a situation where the visual representation of text differs from its actual content. This creates a potential for visual spoofing attacks where malicious actors can manipulate how text appears to users while the underlying data remains unchanged, effectively creating a deceptive interface that can mislead users about the true content being displayed.
From an operational perspective, this vulnerability poses significant security risks in environments where users may encounter untrusted text content from various sources. The attack vector typically involves remote delivery of malicious text content through email, web pages, or file transfers that contain carefully constructed Unicode sequences. Users interacting with such content in Terminal may be deceived into believing they are reading one message while actually viewing a different, potentially malicious message. This type of attack can be particularly dangerous in security-sensitive contexts where users rely on accurate text representation for decision-making processes, such as reviewing system logs, examining network traffic, or analyzing security alerts.
The vulnerability maps to CWE-157 in the Common Weakness Enumeration catalog, which specifically addresses issues related to incorrect handling of input validation and sanitization of formatting characters. This weakness classifies the issue under improper input sanitization and demonstrates how Unicode character handling can create security vulnerabilities when not properly managed. The attack pattern aligns with techniques described in the MITRE ATT&CK framework under the T1059.007 sub-technique for 'Command and Scripting Interpreter: JavaScript' and T1566.001 for 'Phishing: Spearphishing Attachment', as attackers can craft malicious text sequences that appear legitimate but contain hidden directional override characters designed to deceive users into trusting false content representations.
Mitigation strategies for this vulnerability include immediate application of Apple's security patches and updates to macOS version 10.11 or later, which contain the necessary fixes for proper directional override character handling. Organizations should also implement additional security measures such as configuring Terminal applications to use more restrictive text rendering modes that prevent the display of certain Unicode formatting characters, particularly in high-security environments. Network administrators can deploy content filtering solutions that scan for and block suspicious character sequences, while users should be trained to recognize potential spoofing attempts and verify content through multiple independent sources. System administrators should also consider implementing terminal session logging and monitoring to detect unusual text rendering behaviors that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper Unicode handling in security-critical applications and the need for comprehensive input validation across all text processing components.