CVE-2007-3896: Windows Shell32 URL handler input validation flaw enables code execution

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 20 September 2026. Confidence: medium.

high priorityCVSS 2.0 base score is 9.3 with complete confidentiality, integrity and availability impact, and EPSS is near the top percentile, though the affected platforms are legacy and KEV does not list it.

What it is

Shell32.dll in the Windows shell on Windows XP and Server 2003 with Internet Explorer 7 installed mishandles invalid "%" sequences in mailto: and other URI handlers, allowing remote attackers to execute arbitrary programs. Because the flaw sits in a core shell component reached through common URI schemes, it is broadly exposed and rated 9.3 under CVSS 2.0. The record notes possible overlap with CVE-2007-3845 and separate but related issues in the applications that handle the invoked URIs.

Impact

An attacker can cause arbitrary programs to run on the victim's machine, giving code execution in the context of the logged-on user. That enables malware installation, data theft or further lateral movement from the affected host.

Attack surface

Reached remotely over the network through a crafted mailto: or other URI handler, typically delivered via a web page, email or document that invokes the handler. No authentication is required, but the CVSS vector shows medium attack complexity (AC:M), and some user interaction is implied since a handler must be invoked.

Exploitation

Not listed in CISA KEV and no reference carries an exploit tag, but EPSS is high at roughly 0.538 (99th percentile), indicating substantial predicted exploitation activity. The record does not confirm public exploit code or in-the-wild use.

What to do

• Apply the Microsoft security update associated with advisory 943521 (MS07-061) to affected Windows XP and Server 2003 systems.
• Upgrade or retire Windows XP and Server 2003 hosts, which are long past end of support and cannot receive current fixes.
• Restrict or disable unnecessary URI protocol handlers and review mailto: and similar handler registration on remaining hosts.
• Harden browsers and mail clients to block automatic invocation of external URI handlers, and keep IE and dependent applications patched.
• Limit user privileges so successful code execution does not immediately yield administrative rights.

Detection

• Monitor process creation events for unexpected child processes spawned by browsers, mail clients or shell handlers.
• Alert on command lines containing malformed percent-encoding or unusual URI scheme strings passed to handler processes.
• Review proxy, IDS and email gateway logs for mailto: or other URI handler payloads with invalid "%" sequences.
• Audit registry handler registrations and browser helper objects for unexpected or modified URI handler entries.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.