CVE-2007-5456 in Internet Explorer
Summary
by MITRE
Microsoft Internet Explorer 7 and earlier allows remote attackers to bypass the "File Download - Security Warning" dialog box and download arbitrary .exe files by placing a ? (question mark) followed by a non-.exe filename after the .exe filename, as demonstrated by (1) .txt, (2) .cda, (3) .log, (4) .dif, (5) .sol, (6) .htt, (7) .itpc, (8) .itms, (9) .dvr-ms, (10) .dib, (11) .asf, (12) .tif, and unspecified other extensions, a different issue than CVE-2004-1331. NOTE: this issue might not cross privilege boundaries, although it does bypass an intended protection mechanism.
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Analysis
by VulDB Data Team • 07/29/2021
This vulnerability in Microsoft Internet Explorer 7 and earlier versions represents a critical security flaw that undermines the browser's file download protection mechanisms. The issue stems from how Internet Explorer handles file extensions and MIME type detection during download operations, specifically when processing executable files with question mark delimiters followed by non-executable file extensions. The vulnerability allows attackers to circumvent the intended security warning dialog that typically appears when users attempt to download executable files, effectively bypassing a fundamental protection mechanism designed to prevent automatic execution of potentially malicious software.
The technical implementation of this flaw involves the manipulation of URL structures where an executable file extension is followed by a question mark and then another file extension that is not executable. This technique exploits the browser's interpretation of file types and security policies, allowing malicious actors to disguise executable files as benign documents. The vulnerability affects a wide range of file extensions including .txt, .cda, .log, .dif, .sol, .htt, .itpc, .itms, .dvr-ms, .dib, .asf, .tif, and numerous others, demonstrating the broad scope of the issue across multiple file type categories. This approach differs significantly from CVE-2004-1331, indicating a distinct attack vector that specifically targets the download security warning bypass mechanism rather than other aspects of file handling or execution.
From an operational impact perspective, this vulnerability creates significant risks for end users and organizations as it enables the automatic download and execution of malicious executables without user awareness or consent. The bypass of the security warning dialog represents a fundamental failure in the browser's security model, potentially allowing attackers to deploy malware, trojans, or other malicious software without triggering the expected user prompts that would normally alert them to the danger. This issue could be particularly dangerous in corporate environments where users might unknowingly download and execute harmful files, potentially leading to complete system compromise, data exfiltration, or lateral movement within network infrastructures. The vulnerability's potential to cross privilege boundaries, though noted as uncertain, suggests it could enable more severe attacks than initially apparent.
Organizations should implement immediate mitigations including disabling automatic downloads, implementing strict content filtering policies, and educating users about the risks of downloading files from untrusted sources. Browser security updates and patches from Microsoft should be deployed immediately to address this vulnerability. Network-level protections such as web application firewalls and deep packet inspection can help detect and block malicious download attempts. Security professionals should also consider implementing behavior-based monitoring to detect anomalous download patterns that might indicate exploitation attempts. This vulnerability aligns with attack patterns described in the mitre ATT&CK framework under the 'Execution' and 'Defense Evasion' tactics, specifically targeting the 'Exploitation for Client Execution' and 'Obfuscated Files or Information' techniques. The issue also relates to CWE-20, 'Improper Input Validation', and CWE-120, 'Buffer Copy without Checking Size of Input', as it involves improper handling of file extension validation and input processing within the browser's download mechanism.