Eight of the bulletins and 12 of the vulnerabilities were rated "critical" by the company. Three bulletins detailed fixes for "important" flaws, while one described a flaw of moderate severity. The vulnerabilities disclosed Tuesday affect several Microsoft products, including Internet Explorer (IE), Windows Media Player, Microsoft Outlook and PowerPoint.
Tuesday's announcement is "certainly one that people need to sit up and take notice of," said Michael Sutton, director of VeriSign Inc.'s iDefense Labs. He also noted that most of the critical flaws disclosed Tuesday are on the client side, highlighting a continuing trend away from server-side security issues.
"Client-side vulnerabilities have become one of the most prominent methods by which computers become infected today," Oliver Friedrichs, director of Symantec Corp.'s security response group, said in a statement. "Today's release continues that trend" and highlights the danger users face simply by visiting certain Web sites, he said.
One of the bulletins rated as critical by Microsoft described a cumulative upgrade for Internet Explorer that fixed eight newly discovered flaws in the company's Web browser. The impact of the flaws included remote code execution, information disclosure and user spoofing, according to Microsoft.
Another bulletin offers a fix for a critical vulnerability in how Windows handles the ART image format used by America Online Inc.'s client software. An attacker could exploit the flaw by creating a specially crafted ART image that would allow for remote-code execution on a victim's computer.
Another critical remote-code execution vulnerability disclosed Tuesday involves Microsoft Windows Media Player technology. The buffer-overflow flaw exists in the way Media Player handles the Portable Network Graphics (PNG) image format associated with Media Player and could allow an attacker to take complete control of an affected system, the company warned.
In addition, security administrators should pay particular attention to vulnerabilities detailed in bulletin MS06-25 and MS06-29, according to an advisory from McAfee Inc.
The flaws described in MS06-25 affect the Windows Routing and Remote Access Service, while those described in MS06-29 deal with a script-injection vulnerability in Exchange Server.
"These vulnerabilities are worm candidates and could result in a mass-mailing worm," McAfee said.
Microsoft also announced fixes for several other flaws in products such as PowerPoint and Word.
In an e-mailed statement, Monty Ijzerman, senior manager of the global threat group at McAfee Avert Labs, said the number of critical flaws patched by Microsoft in the first half of 2006 is 70 percent higher than during the same period last year.