1,900 Sign customers’ telephone numbers uncovered by Twilio phishing

Signal's security-minded messaging app is dealing with a third-party phishing attempt that exposed a small number of users' phone numbers.
Enlarge / Sign’s security-minded messaging app is coping with a third-party phishing try that uncovered a small variety of customers’ telephone numbers.

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A profitable phishing assault at SMS providers firm Twilio could have uncovered the telephone numbers of roughly 1,900 customers of the safe messaging app Sign—however that is in regards to the extent of the breach, says Sign, noting that no additional consumer information might be accessed.

In a Twitter thread and assist doc, Sign states {that a} latest profitable (and deeply resourced) phishing assault on Twilio allowed entry to the telephone numbers linked with 1,900 customers. That is “a really small share of Sign’s complete customers,” Sign writes, and all 1,900 affected customers might be notified (by way of SMS) to re-register their units. Sign, like many app firms, makes use of Twilio to ship SMS verification codes to customers registering their Sign app.

With momentary entry to Twilio’s buyer assist console, attackers may have probably used the verification codes despatched by Twilio to activate Sign on one other system and thereby ship or obtain new Sign messages. Or an attacker may affirm that these 1,900 telephone numbers had been really registered to Sign units.

No different information might be accessed, largely due to Sign’s design. Message historical past is saved fully on consumer units. Contact and block lists, profile particulars, and different consumer information require a Sign PIN to entry. And Sign is asking customers to allow registration lock, which prevents Sign entry on new units till the consumer’s PIN is appropriately entered.

“The sort of telecom assault suffered by Twilio is a vulnerability that Sign developed options like registration lock and Sign PINs to guard towards,” Sign’s assist doc reads. The messaging app notes that whereas Sign does not “have the power to immediately repair the problems affecting the telecom ecosystem,” it should work with Twilio and different suppliers “to tighten up their safety the place it issues for our customers.”

Sign PINs had been launched in Could 2020, partly to de-emphasize the reliance on telephone numbers as a main consumer ID. This newest incident could present one other nudge to de-couple Sign’s robust safety from the SMS ecosystem, the place low cost, efficient spoofing and broad community hacks stay all too frequent.


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