Phishers who breached Twilio and fooled Cloudflare could easily get you, too

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At least two security-sensitive firms—Twilio and Cloudflare—had been focused in a phishing assault by a sophisticated risk actor who had possession of dwelling telephone numbers of not simply staff however staff’ relations as nicely.

In the case of Twilio, a San Francisco-based supplier of two-factor authentication and communication companies, the unknown hackers succeeded in phishing the credentials of an undisclosed variety of staff and, from there, gained unauthorized entry to the corporate’s inside techniques, the corporate stated. The risk actor then used that entry to information in an undisclosed variety of buyer accounts.

Two days after Twilio’s disclosure, content material supply community Cloudflare, additionally headquartered in San Francisco, revealed it had additionally been focused in an analogous method. Cloudflare stated that three of its staff fell for the phishing rip-off, however that the corporate’s use of hardware-based MFA keys prevented the would-be intruders from accessing its inside community.

Well-organized, subtle, methodical

In each instances, the attackers in some way obtained the house and work telephone numbers of each staff and, in some instances, their relations. The attackers then despatched textual content messages that had been disguised to look as official firm communications. The messages made false claims corresponding to a change in an worker’s schedule, or the password they used to log in to their work account had modified. Once an worker entered credentials into the faux web site, it initiated the obtain of a phishing payload that, when clicked, put in distant desktop software program from AnyDesk.



The risk actor carried out its assault with virtually surgical precision. When the assaults on Cloudflare, at the very least 76 staff acquired a message within the first minute. The messages got here from quite a lot of telephone numbers belonging to T-Mobile. The area used within the assault had been registered solely 40 minutes prior, thwarting the area safety Cloudflare makes use of to ferret out impostor websites.


“Based on these factors, we have reason to believe the threat actors are well-organized, sophisticated, and methodical in their actions,” Twilio wrote. “We have not yet identified the specific threat actors at work here, but have liaised with law enforcement in our efforts. Socially engineered attacks are—by their very nature—complex, advanced, and built to challenge even the most advanced defenses.”

Matthew Prince, Daniel Stinson-Diess, Sourov Zaman—Cloudflare’s CEO, senior safety engineer and incident response chief respectively—had an analogous take.

“This was a sophisticated attack targeting employees and systems in such a way that we believe most organizations would be likely to be breached,” they wrote. “Given that the attacker is targeting multiple organizations, we wanted to share here a rundown of exactly what we saw in order to help other companies recognize and mitigate this attack.”

Twilio and Cloudflare stated they do not know how the phishers obtained worker numbers.

It’s spectacular that regardless of three of its staff falling for the rip-off, Cloudflare saved its techniques from being breached. The firm’s use of hardware-based safety keys that adjust to the FIDO2 normal for MFA was a crucial purpose. Had the corporate relied on one-time passwords from despatched textual content messages and even generated by an authentication app, it possible would have been a unique story.

The Cloudflare officers defined:

When the phishing web page was accomplished by a sufferer, the credentials had been instantly relayed to the attacker by way of the messaging service Telegram. This real-time relay was vital as a result of the phishing web page would additionally immediate for a Time-based One Time Password (TOTP) code.

Presumably, the attacker would obtain the credentials in real-time, enter them in a sufferer firm’s precise login web page, and, for a lot of organizations that may generate a code despatched to the worker by way of SMS or displayed on a password generator. The worker would then enter the TOTP code on the phishing web site, and it too can be relayed to the attacker. The attacker could then, earlier than the TOTP code expired, use it to entry the corporate’s precise login web page — defeating most two-factor authentication implementations.


We confirmed that three Cloudflare staff fell for the phishing message and entered their credentials. However, Cloudflare doesn’t use TOTP codes. Instead, each worker on the firm is issued a FIDO2-compliant safety key from a vendor like YubiKey. Since the arduous keys are tied to customers and implement origin binding, even a classy, real-time phishing operation like this can not collect the knowledge essential to log in to any of our techniques. While the attacker tried to log in to our techniques with the compromised username and password credentials, they could not get previous the arduous key requirement.

Cloudflare went on to say it wasn’t disciplining the workers who fell for the rip-off and defined why.


“Having a paranoid but blame-free culture is critical for security,” the officers wrote. “The three employees who fell for the phishing scam were not reprimanded. We’re all human and we make mistakes. It’s critically important that when we do, we report them and don’t cover them up.”


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