In January, we released a study showing the ease of SIM swaps at five U.S. prepaid carriers. These attacks—in which an adversary tricks telecoms into moving the victim’s phone number to a new SIM card under the attacker’s control—divert calls and SMS text messages away from the victim. This allows attackers to receive private information such as SMS-based authentication codes, which are often used in multi-factor login and password recovery procedures.
We also uncovered 17 websites that use SMS-based multi-factor authentication (MFA) and SMS-based password recovery simultaneously, leaving accounts open to takeover from a SIM swap alone; an attacker can simply reset a victim’s account password and answer the security challenge when logging in. We responsibly disclosed the vulnerabilities to those websites in early January, urging them to make changes to disallow this configuration. Throughout the process, we encountered two wider issues: (1) lack of security reporting mechanisms, and (2) a general misunderstanding of authentication policies. As a result, 9 of these 17 websites, listed below, remain vulnerable by default.
Disclosure Process. On each website, we first looked for email addresses dedicated to vulnerability reporting; if none existed, we looked for the companies on bug bounty platforms such as HackerOne. If we were unable to reach a company through a dedicated security email or through bug bounty programs, as a last resort, we reached out through customer support channels. Sixty days after our reports, we re-tested the configurations at the companies, except for those that reported that they had fixed the vulnerabilities.
Outcomes. Three companies—Adobe, Snapchat, and eBay—acknowledged and promptly fixed the vulnerabilities we reported. In one additional case, the vulnerability was fixed, but only after we exhausted the three contact options and reached out to company personnel via a direct message on Twitter. In three cases—Blizzard, Microsoft, and Taxact—our vulnerability report did not produce the intended effect (Microsoft and Taxact did not understand the issue, Blizzard provided a generic acknowledgment email), but in our 60-day re-test, we found that the vulnerabilities had been fixed (without the companies notifying us). As such, we do not know whether the fixes were implemented in light of our research.
Read the full post at Freedom to Tinker.