Google has issued patches for two new Stagefright-related vulnerabilities, one of which affects Android versions going back to 2008 and puts millions of users at risk.
The flaws were found by security company Zimperium, which also unearthed the original Stagefright flaws in April.
In an advisory Monday, Google said it didn't appear that attackers have started exploiting the vulnerabilities yet.
The latest flaws are only slightly less dangerous than their predecessors, which allowed a device to be compromised merely by sending a specially crafted multimedia message (MMS). An attacker needed only to know the victim's phone number.
To exploit the latest flaws, dubbed Stagefright 2.0, an attacker would have to convince a user to visit a website and play a piece of audio or video content.
The vulnerabilities relate to problems with how Android processes metadata within that content, Zimperium said in a blog post.
Google has released an over-the-air update for its Nexus Android devices and had notified its partners of the issues by Sept. 10, the company said.
Zimperium held off releasing proof-of-concept exploit code but will allow some of its partners to see it later this month, it said.
In light of the number of users affected by Stagefright, Google said in August it would begin issuing monthly security patches, mirroring steps taken years ago by companies including Microsoft for desktop software.
Still, fixing software problems on mobile devices is a disjointed affair and users are dependent on device manufacturers and operators for timely patching. After Google's announcement, major manufacturers including Samsung and LG also committed to monthly patching.