Attack code for old Firefox bug hits the net

Computer code that demonstrates how a known flaw in an older version of the Firefox or Mozilla web browsers can be exploited in a potentially crippling attack was published on the web over the weekend.

The vulnerability was fixed in Firefox 1.0.5, released in July, and in Mozilla Suite 1.7.9, according to Mozilla.

The code was published by Aviv Raff, a developer in Israel. Writing in his blog on Sunday he said: "I think it's been enough time for people to upgrade from v1.0.4 of Firefox." Raff's code doesn't do much harm but he notes that it would be easy to turn it into malicious code that commandeers a vulnerable system.

The vulnerability is in the way the web browsers handle JavaScript, according to a Mozilla alert dated 12 July, the day Firefox 1.0.5 was released. An attacker could craft a malicious website that, when accessed by a vulnerable PC, could let a attacker run code on that system without the owner realising it.

Mozilla has released several updates to both Firefox and the Mozilla Suite since July. The latest version of Firefox is 1.5, released late last month. A security vulnerability that could cause the browser to appear to hang has already been pinpointed in that version but Mozilla says it is a minor problem.

In other browser news, Microsoft on Tuesday released a patch that fixes four vulnerabilities in Internet Explorer. The software maker deems two of the flaws "critical". One is already being used to attack IE users, Microsoft said in a bulletin.

Secunia is warning of a security flaw in version 8.01 of the Opera web browsers. Earlier versions may also be affected, the security monitoring company said in an alert on Tuesday. The flaw lies in the way the browser handles mouse clicks in new windows and in how it displays a dialogue box for downloads, according to Secunia's advisory.

The Opera flaw could be exploited to trick people into downloading malicious programs, Secunia said. The company advised people to upgrade to Opera 8.0.2, which has been available since late July.

Joris Evers writes for CNET News.com