Yahoo patches vulnerability allowing hackers to eavesdrop on emails
Yahoo has fixed a flaw in its Mail service that could have allowed hackers to eavesdrop on user emails nearly a year after the same bug was disclosed and patched. Jouko Pynnonen from Finland received $10,000 from Yahoo for disclosing the new vulnerability, which Yahoo fixed last month.
The flaw concerned a cross-site scripting attack that gave an attacker the permission to read a user’s email or create a virus to infect Yahoo Mail accounts. Pynnonen explained that a user must view the email from an attacker for the bug to work.
The bug was similar to an old Yahoo Mail flaw that Pynnonen discovered last year that could give hackers complete control of a Yahoo Mail account.
Shortcoming in Yahoo filters
The researcher discovered the flaw in the email composing view, where various attachment options called his attention to potential bug in basic HTML filtering. Pynnonen then created an email with various attachments and sent the message to an external mailbox. Upon inspecting the raw HTML contained in the email, some malicious attributes caught his attention.
“What caught my eye were the data-* HTML attributes. First, I realised my last year’s effort to enumerate HTML attributes allowed by Yahoo’s filter didn’t catch all of them.”
Pynnonen thought it was possible to embed several HTML attributes that would pass through Yahoo’s HTML filter. He eventually found a pathological case after composing an email with abusive data-* attributes.
Yahoo has been under fire earlier this year following reports that indicate at least 200 million Mail accounts were sold on the dark web.
- How to sign into Windows 10 Mail with a Yahoo account
- Yahoo Mail app for Windows 10 now syncs contacts with Microsoft People
Microsoft is all set to launch its next big update, Windows 10 version 1809 in October. While that should be a nice piece of news […]
The Windows 10 October 2018 Update (otherwise 18H2) rollout might now be two to three weeks away. For the last few months, new build previews […]