Sunday, March 2, 2014

[securityaffairs] Critical flaw in Yahoo allows Hacker to delete 1.5M records

Vulnerability in Yahoo allowed Egyptian hacker to delete more than 1 million and half records from Yahoo database. Yahoo immediately fixed it.

The Egyptian cyber security expert Ibrahim Raafat has discovered a serious flaw  in the Yahoo! website.
The hacker demonstrated on his blog how to exploit the “Insecure Direct Object Reference Vulnerability” vulnerability in the Yahoo! sub-domain ( to delete all the posted thread and comments on Yahoo’s Suggestion Board website.

Yahoo question-300x114

As demonstrated by Raafat it is possible to escalate user privileges that allow a hacker to delete more than 365,000 posts and 1,155,000 comments from Yahoo! Database. Following the video Proof-of-Concept for the Yahoo! vulnerability.

It is not first time that hackers discover a serious flaw in the websites managed by the company, last year for example another Egyptian experts, Ebrahim Hegazy@Zigoo0), has found Blind SQL Injection could lead to data leakage.
Technical details on how to exploit the flaw to delete comments and posts are available in the post published by the expert.
Deleting Comments
Ibrahim, while deleting his comment, has noticed the HTTP Header of POST request, i.e.
There are 5 parameters in the above URL
prop= category
fid= topic id
crumb = something like session
cid = Comment id
cmd= the method
He has found that changing the FID and CID parameter values he was able to delete other comments from the forum, even if posted by other users.

Deleting Posts
Ibrahim also discovered a similar problem testing the deletion mechanism, the HTTP Header POST request for deleting action appears as:
POST cmd=delete_item&crumb=SbWqLz.LDP0
but just appending the fid (topic id) parameter to the URL is possible to delete the respective post, anyone who has posted
POST cmd=delete_item&crumb=SbWqLz.LDP0&fid=xxxxxxxx
Ibrahim has reported the flaw to Yahoo Security team
Starting from the knowledge of the vulnerabilities also a novice hacker could write a script that interactively erases posts and comments from the Yahoo! sub-domain.
The vulnerability was reported to Yahoo! company that has fixed it and rewarded the expert with Bug Bounty.

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