Signal, a cross-platform centralized encrypted instant messaging service declares that a data breach at Cloud Communication Company Twilio exposed almost 1,900 Signal users’ phone numbers.
Twilio provides phone number verification services for Signal and notably on August 4th, it disclosed that attackers hacked its network.
“All users can rest assured that their message history, contact lists, profile information, whom they’d blocked, and other personal data remain private and secure and were not affected”, Signal
According to the recent advisory published by Signal, an attacker gained access to Twilio’s customer support console via phishing. Nearly 1,900 users’ phone numbers were exposed as being registered to a Signal account and the SMS verification code used to register with Signal was also revealed.
Signal says attackers only attempt to register the phone numbers they accessed to another device using the SMS verification code. The attacker no longer has this access, and Twilio has shut the attack down.
“Importantly, this did not give the attacker access to any message history, profile information, or contact lists”, Signal.
Signal mentions that the attack is due to the vulnerability that Signal developed features like registration lock and Signal PINs to protect against.
The company encourages users to enable registration lock for their Signal account. Go to Signal Settings (profile) > Account > Registration Lock to do this.
Signal PIN is a code used to support features like non-phone number-based identifiers. By using your PIN, you can recover your profile, settings, contacts, and who you’ve blocked if you ever lose or switch devices.
“Signal does not have access to your message history, contact list, profile information, which you’ve blocked, and other personal data. And this information certainly is not available to Twilio, or via the access temporarily gained by Twilio’s attackers”, Signal
Notifying the Affected Users
The company ensures as of August 16th, they will completely notify all the affected users via SMS about the hack and inform them how to protect their accounts.
The company sends the SMS message: “This is from Signal Messenger. We’re reaching out so you can protect your Signal account. Open Signal and register again. More info: https://signal.org/smshelp“