Microsoft's Word 2003 and Excel 2003 can be crashed by attackers who feed the business applications malformed documents, security firm Symantec has warned.
In separate alerts, Symantec warned that the bugs -- both discovered and disclosed by a Russian researcher with the moniker "Sehato" -- could be exploited by attackers to bring down the Office applications.
"A remote attacker may exploit this vulnerability by presenting a malicious WMF file to a victim user," Symantec's report on the Office 2003 flaw said. "The issue is triggered when the application is used to insert the malicious file into a document."
Specially crafted Windows Metafile (WMF) image files were the root of a major attack in late 2005 and early 2006 that was launched from hundreds of malicious websites and compromised thousands of PCs. This bug seems to be different from the 2005/2006 vulnerability.
The Excel flaw can be leveraged by a malformed spreadsheet file rather than a WMF image, Symantec added.
Attacks using either vulnerability require users to download malicious files from a website or open them when they arrive as emailed file attachments.
The Explorer file interface in Windows XP and Windows Server 2003 is also vulnerable, Symantec said, adding that Explorer will crash when attempting to open a malformed WMF image – another bug divulged by Sehato.
Microsoft did not respond to requests for a comment on the new threats.
Problems with Microsoft's Office software have been endemic since early 2006, and there are no signs that hackers and researchers have emptied its well of vulnerabilities.
During 2006 Microsoft issued 13 security updates for Office 2000 and 11 for Office 2003. In the first two months of 2007, it released four bulletins for Office 2000 and six for Office 2003.
Earlier this week, researchers uncovered the second major flaw in Office 2007.