How do SMS sign-in links put user data at risk?

SMS sign-in links are delivered via unencrypted text messages, making them vulnerable to interception. Authentication systems that accept these links as sufficient proof of identity can allow unauthorized access to sensitive personal information.

Can attackers guess valid SMS login links?

Yes, some services use weak tokens in their SMS links, which attackers can exploit to guess valid URLs and gain access to other users' accounts.

What are services doing about SMS security weaknesses?

Many online services have not adequately addressed reported SMS security weaknesses, with most offering no public response or corrective actions, despite significant user data exposure risks.

Home / Technology / Convenient SMS Logins Leave Accounts Vulnerable

Convenient SMS Logins Leave Accounts Vulnerable

28 Jan

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Summary

SMS sign-in links are insecure, exposing personal data.
Weak tokens allow attackers to guess valid links.
Many services ignore reported security weaknesses.

Convenient SMS Logins Leave Accounts Vulnerable

Online services increasingly rely on SMS sign-in links for easier account access, bypassing traditional passwords. However, this convenience comes at a significant security cost. SMS messages are transmitted unencrypted, making them vulnerable to interception and exposure.

A recent technical review examined millions of SMS messages linked to hundreds of digital services. It found that authentication systems treating SMS-delivered URLs as sufficient proof of identity allow unauthorized access to private user information. Some services also used weak tokens, enabling attackers to guess valid links and access accounts.

Furthermore, the review noted that some links remained active for extended periods, increasing the risk window. Mismatches in data requests also led to overfetching personal information. Despite contact from researchers, most providers failed to acknowledge or fix these widespread weaknesses, leaving millions of users exposed.

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