Code for both the vulnerabilities has been published, but there have been no reports of attacks taking advantage of the flaws, the SANS Internet Storm Center, which monitors network threats, said in an advisory released Wednesday.
SANS initially reported that one of the flaws also affected Mozilla's Firefox Web browser, but on Friday it said in an updated advisory that it had determined, after further research, that Firefox was not affected by it.
The first issue is related to the handling of a technology that is used to access documents delivered from one Web site to another, according to the advisory.
Attackers could exploit the IE flaw using cross-site scripting, said Monty Ijzerman, senior manager of McAfee's Global Threat Group. That technique enables hackers to view the contents of one open browser from a second browser open on the user's system. The attackers, as a result, could swipe sensitive information, such as online banking data, from one of the sites showing.
"We consider this flaw less serious than the other IE flaw," Ijzerman said. "A user would have to have multiple browsers open, and the information on the site would have to be relevant to what the attacker wanted."
The second security hole is related to the way HTA applications are processed. (This flaw is the one that SANS at first thought also existed in Firefox.)
A PC user could be tricked into double-clicking on a malicious file and remote code could be executed, Ijzerman said. An attacker could exploit the vulnerability to read files on a system or to install rootkits, which make system changes to hide another piece of possibly malicious software.
The two IE security flaws come as Microsoft, which is designed to offer more security features. SANS said Friday that IE7 does not have the security holes.
Microsoft said it is investigating the issues and has yet to hear of any attackers exploiting the reported vulnerabilities.
CNET News.com's Caroline McCarthy contributed to this story.