A vulnerability in the Snapchat app allows attackers to flood the device with information, freezing and crashing the users iPhone, according to security researcher Jaime Sanchez.

Using a flaw in how the app authenticates users, Sanchez discovered that sending a huge number of messages to one user will cause their iPhone to crash. Even once it powers back up, the app itself still hangs until the attack is over.

Sanchez, who works for O2’s parent company Telefonica, disclosed the vulnerability on Saturday, and found that the company had banned his two testing accounts and blocked the IP he used to demonstrate the attack – but had not immediately fixed the actual problem.

The flaw is based on the way Snapchat authenticates users: rather than sending passwords with each picture, it sends an authentication token based on the password and the time. In theory, this lets the site’s servers reject individual requests.

In practice, however, instead of demanding a new access token for every action, the app’s servers will accept re-used tokens. While the actual Snapchat app still generates new tokens each time, an attacker can generate one legitimate token, and then use it to automatically send messages.

That means that the only limit to how many times a message can be sent is the speed with which the attacker’s computer can send requests to Snapchat’s servers, allowing Sanchez to use several computers at once to send a thousand messages to one phone in five seconds, causing it to crash.



This is the second security breach at Snapchat in 2014. In August 2013, another group of researchers disclosed a vulnerability that let users find the Snapchat username associated with any phone number. Four months later, the vulnerability still hadn’t been fixed, and on January 1, 4.6m mobile numbers were leaked by hackers. The company delayed fixing the issue – and apologising for the leak – for a further eight days.

Snapchat did not immediately reply to a request for comment.

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