Researchers built a WeChat worm that hijacks accounts while the phone is still ringing

Memory corruption in the VoIP stack, reached by placing a call ^[1]. The exploit runs while the handset rings and completes in seconds ^[6]. Picking up does not interrupt it, and the person who answers hears nothing ^[2]. Declining ends that attempt only; per Calif, the attacker calls back later, for example while the target is asleep ^[2].

The one gate is membership of the victim's WeChat friend list ^[3]. Calif built the demo to show that the gate opens from the inside: "an attacker can compromise one of your friends first and use their account to reach you," the researchers wrote, and the extra trust WeChat extends to contacts then works for the attacker ^[4]. The chain ran once in the lab, from a Pixel 10a to an iPhone 17e and on to a second Pixel 10a ^[5].

On its own, the bug takes the account, not the phone ^[7]. Calif says it can be chained with separate Android or iOS vulnerabilities to reach broader device control ^[7], and The Hacker News notes that Calif's post describes routes an attacker could use rather than routes it tested ^[8]. Nothing published shows the worm crossing out of WeChat into the handset. What it does show is a self-propagating account takeover, and for many users that account holds payments, official accounts and mini programs inside the same app ^[27].

Calif dates its own work: the engineering team knew of the bug on 23 July, finished an Android exploit on 30 July, an iOS exploit on 2 August, and a cross-platform worm demo on 11 August ^[9][10]. That is 19 calendar days from bug to worm ^[25]. The public framing is about two days from discovery to first RCE with AI help, plus another week for the worm, or roughly nine ^[11]; the post does not say whether the shorter figures count working time only ^[12]. Tencent's client releases landed 29 days after the 23 July date, and the server-side block was confirmed at 36 ^[26]. Calif shared its complete analysis and working exploits with Tencent on 3 September, after both ^[15].

Tencent reported 1.439 billion combined monthly active users for Weixin and WeChat as of 30 June 2026 ^[22]. Calif's report says actors "can compromise over a billion phones (or accounts), upending livelihoods and breaking communities worldwide" ^[23], and the firm says it published to push governments and technology companies toward cooperation on AI security ^[24]. Tencent's own contribution to the record is thinner: the iOS release notes and App Store entry describe 8.0.76 as bug fixes, and the most recent post on its security response site is dated April 2022 ^[17]. No attacks using the flaw have been reported, and Calif does not claim any ^[21].

Seven days from bug awareness to a working Android RCE against a widely deployed VoIP stack is the figure in Calif's timeline that stands whatever share of the credit AI gets ^[31].