Security Experts:

Flaws Allowed Hackers to Brute-Force Instagram Accounts

A researcher received a $5,000 bounty from Facebook after finding two vulnerabilities that could have allowed hackers to brute-force Instagram account passwords.

Belgian bug bounty hunter Arne Swinnen discovered that malicious actors could launch brute force attacks against Instagram accounts via the official Android application and via the registration page on instagram.com.

The first vulnerability, which Swinnen reported to Facebook in late December, could have been exploited to conduct brute force attacks against the authentication domain used by the Instagram app for Android.

The researcher found that the authentication system allowed 1,000 guesses from one IP address before displaying a message that the username does not exist. However, this message was only displayed until the 2,000th attempt, and from there on the system started providing one reliable response (i.e. the password is correct or incorrect) and one unreliable response (i.e. user not found).

According to Swinnen, an attacker could have created a script that simply replayed the unreliable responses until a reliable response was obtained. The expert developed a script that tested 10,001 passwords against a test account.

Furthermore, the test showed that an attacker could have logged in to the compromised account from the same IP address that was used to brute-force the password, which indicated that security controls designed to protect accounts against unauthorized logins had not been in place.

The second vulnerability, reported by Swinnen in February, affected the registration page from the Instagram website.

The researcher registered a test account and captured the request sent during registration to Instagram servers. When he replayed the exact same request, he received a response containing the message “Those credentials belong to an active Instagram account.”

Since there was no rate limitation in place, an attacker could create a script that sent out requests with various passwords for a targeted username. If the response returned a “fail” status, the password was incorrect, but if the response contained the message saying that the credentials belonged to an active account, the password was correct.

Facebook addressed both issues by limiting the number of login attempts. The researcher said the company also made some slight improvements to its password policy to prevent users from setting passwords such as “password” and “123456.”

The social media giant awarded the researcher a combined bounty of $5,000 for the two vulnerabilities.

Swinnen noted that brute force attacks against Instagram accounts pose a serious threat to the service’s more than 400 million users considering that two-factor authentication (2FA) is only now being rolled out, password policies are fairly weak, there are no security controls in place, and usernames can be easily enumerated.

Swinnen is not the only bug bounty hunter who has found serious vulnerabilities in Instagram. A few weeks ago, a 10-year-old from Finland got $10,000 from Facebook after discovering a flaw that allowed anyone to easily delete comments on Instagram.

Related: Facebook Pays Out $7,500 Bounty for Account Hijacking Flaw

Related: Facebook Password Reset Flaw Earns Researcher $15,000

Related: Facebook, Researcher Quarrel Over Instagram Hack

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.