Security researchers have discovered a serious boundary error vulnerability in multiple versions of Microsoft's Windows platform and warned that attackers could hijack systems via Windows Explorer and Internet Explorer (IE).

Rodrigo Gutierrez, a researcher with Trustix AS, notified Microsoft of the flaw with a warning that it could be exploited by malicious attackers to cause a buffer overflow and lead to system takeover.

Microsoft confirmed Gutierrez's findings in an advisory and recommended users install the latest service packs for Windows XP and Windows 2000. The software giant said the hole was fixed in the service packs but independent security consultants Secunia said the vulnerability "has been confirmed on fully patched systems running Windows XP and Windows 2000."

Secunia rates the flaw as "highly critical" and urged Windows XP and Windows 2000 users to restrict traffic in border routers and firewalls as a temporary workaround. Users could also disable the "Client for Microsoft Networks" for network cards to impact file sharing functionality.

The flaw also reportedly affects Windows 95, 98, and Me and Secunia said it was unknown whether Windows NT 4.0 and Windows 2003 were at risk.

According to the advisories, the boundary error issue is triggered via Internet Explorer and Windows Explorer when connecting to a file server. This can be exploited to cause a buffer overflow by setting up a malicious share with an overly long name (about 300 bytes) containing no lower case characters.

"Successful exploitation may potentially allow execution of arbitrary code on a user's system but requires that the user is either tricked into connecting to a malicious file server, visit a malicious website, or follow a specially crafted link," Secunia warned.

The Secunia alert listed the affected Microsoft operating systems as Windows XP Pro, Windows XP Home Edition, Windows Millenium, Windows 98 Second Edition, Windows 98, Windows 95, Windows 2000 Server, Windows 2000 Professional, Windows 2000 Datacenter Server and Windows 2000 Advanced Server.

Affected software include IE versions 5.01, 5.5 and 6.0.