Topic: Microsoft IE6 urlmon.dll Long URL Buffer Overflow vulnerability

Release Date: 2006-08-25

CVE CAN ID : CVE-2006-3869

Affected system:
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Internet Explorer 6 SP1 with MS06-042
- Microsoft Windows XP SP1
- Microsoft Windows 2000 SP4

Unaffected system:
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Impact:
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NSFocus Security Team discovered a buffer overflow in IE 6.0SP1 which allows remote code execution via an over-long URL.

Description:
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Security Bulletin MS06-042 released by Microsoft on August 8th, 2006 fixed multiple vulnerabilities, but the update for IE 6 introduced a new vulnerability.

When visiting websites with HTTP/1.1 protocol and data compression enabled, a buffer overflow might occur if an over-long URL is passed to IE 6. This overflow arises due to an incorrect call to function lstrncpyA, possibly resulting in heap data structure corruption. Carefully crafted data might lead to arbitrary code execution.

Attackers might craft a malicious WEB page and allure users to visit it in order to run arbitrary code with the users' privilege. If the user is the administrator, the attacker might gain complete control over the system. Attackers might host malicious web servers of their own, or exploit certain servers that enable HTTP/1.1 protocol and data compression in order to launch attacks.

Workaround:
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* Temporarily disable HTTP 1.1 support in IE.

Vendor Status:
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2006.08.10 Informed the vendor
2006.08.17 Vendor confirmed the vulnerability
2006.08.24 Microsoft released related patch and re-released MS06-042.

Detailed Microsoft Security Bulletin is available at:

http://www.microsoft.com/technet/security/bulletin/MS06-042.mspx

Additional Information:
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The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2006-3869 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems. Candidates may change significantly before they become official CVE entries.

Credit:
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Hu Qianwei of NSFocus Security Team found the vulnerability.