Google Security Flaw Exposed: Risk of Account Takeover and How It Was Fixed

In a significant security revelation, Google has addressed a flaw that could have potentially compromised users’ privacy and security by exposing their account recovery phone numbers. Discovered by Singaporean security researcher “brutecat,” this vulnerability was found in Google’s account recovery feature, which could have been exploited to brute-force a Google account’s recovery phone number. The researcher’s findings have led to a \$5,000 reward from Google and the removal of the vulnerable feature, significantly reducing the risk of exploitation.

A Deeper Dive Into the Vulnerability

The vulnerability existed in Google’s username recovery form, which was used to help users check if a recovery email or phone number was associated with a specific account. The flaw lay in the form’s version that didn’t have proper anti-abuse protections, allowing attackers to send an overwhelming number of requests in a short period, bypassing CAPTCHA-based rate limits. This loophole made it possible for attackers to quickly try all possible phone number combinations and pinpoint the correct digits in a matter of seconds or minutes.

What made the exploit particularly dangerous was that, by targeting a deprecated version of the recovery form (which had no JavaScript), attackers could try multiple permutations of phone numbers without triggering defensive mechanisms. Once the correct phone number was identified, an attacker could use this information to launch a SIM-swapping attack, gaining full access to the victim’s Google account.

Further, the researcher demonstrated that attackers could take advantage of Google’s “Forgot Password” process to learn key details about the victim’s phone number, such as the country code, by accessing a Looker Studio document. This, combined with the brute-forcing method, led to a major breach of privacy and could have serious consequences, including exposing a user’s full name and enabling full account takeover.

What Undercode Say:

The vulnerability unveiled by “brutecat” underscores an important security flaw in Google’s account recovery process. While Google’s overall security infrastructure is robust, this incident highlights that even small loopholes in recovery mechanisms can have significant consequences. This flaw allowed attackers to exploit outdated systems, which had been overlooked in the face of more modern updates.

In a broader context, this incident serves as a reminder of the importance of secure recovery options for online accounts, particularly those that serve millions of users worldwide. While brute-forcing phone numbers via this method was highly technical and required an attacker to know certain details about the victim, the fact that such an attack was possible illustrates how attackers continually exploit even minor weaknesses.

Moreover, the role of responsible disclosure in this situation cannot be overstated. “Brutecat” followed ethical guidelines by reporting the flaw to Google, who acted swiftly to address the issue. Their response—awarding the researcher \$5,000 and removing the affected recovery form—sets an example of how tech companies should engage with the security research community to stay ahead of potential threats.

From a broader perspective, this is part of a growing trend where attackers are increasingly focused on recovery mechanisms, which are often considered secondary features. The rise in SIM-swapping attacks, in particular, emphasizes the need for multi-layered security strategies that go beyond traditional password-based protection.

Fact Checker Results ✅

Vulnerability Validity: The flaw reported by “brutecat” is legitimate and was acknowledged by Google, with the company issuing a \$5,000 bug bounty for the disclosure.
Exploitation Risk: The risk of the vulnerability being exploited was real, particularly for users with easily guessable recovery phone numbers or those lacking additional security layers.
Fix Implementation: Google acted quickly to remove the outdated username recovery form and mitigate the risk, addressing the flaw in June 2025.

Prediction: Future of Account Recovery and Security Enhancements 🔮

Looking ahead, this incident could spur significant changes in how account recovery processes are designed. As attackers focus more on bypassing traditional security layers like CAPTCHA and brute-forcing recovery phone numbers, we may see a broader push towards more sophisticated authentication systems. Multi-factor authentication (MFA), especially involving biometric data, could become a standard for account recovery, reducing reliance on easily compromised recovery methods.

Further, the incident may encourage other tech giants to reevaluate their own account recovery processes and consider the integration of machine learning or AI to detect and prevent suspicious account recovery attempts in real-time. As the digital world becomes increasingly interconnected, ensuring the privacy and security of users’ recovery mechanisms will be crucial in mitigating the risks posed by attackers.