Yahoo Bug Bounty #37 - Sender Spoofing Vulnerability Mar 14 2016 03:33PM
Vulnerability Lab (research vulnerability-lab com)
Document Title:
Yahoo Bug Bounty #37 - Sender Spoofing Vulnerability

References (Source):

Release Date:

Vulnerability Laboratory ID (VL-ID):

Common Vulnerability Scoring System:

Product & Service Introduction:
Yahoo Inc. (styled as Yahoo!) is an American multinational technology company headquartered in Sunnyvale, California. It is globally known
for its Web portal, search engine Yahoo! Search, and related services, including Yahoo! Directory, Yahoo! Mail, Yahoo! News, Yahoo! Finance,
Yahoo! Groups, Yahoo! Answers, advertising, online mapping, video sharing, fantasy sports and its social media website. It is one of the most
popular sites in the United States.[9] According to third-party web analytics providers, Alexa and SimilarWeb, Yahoo! is the highest-read news
and media website, with over 7 billion readers per month, being the fourth most visited website globally, as of June 2015.[8][10][11] According
to news sources, roughly 700 million people visit Yahoo websites every month. Yahoo itself claims it attracts "more than half a billion consumers
every month in more than 30 languages. Yahoo was founded by Jerry Yang and David Filo in January 1994 and was incorporated on March 1, 1995. Marissa
Mayer, a former Google executive, serves as CEO and President of the company.

(Copy of the Homepage: https://en.wikipedia.org/wiki/Yahoo! )

Abstract Advisory Information:
An independent vulnerability laboratory researcher discovered a mail spoofing vulnerability in the official Yahoo classic online service web-application.

Vulnerability Disclosure Timeline:
2015-10-17: Researcher Notification & Coordination (Lawrence Amer)
2015-10-18: Vendor Notification (Yahoo Security Incident Team)
2015-10-25: Vendor Response/Feedback (Yahoo Security Incident Team)
2016-02-29: Vendor Fix/Patch (Yahoo Developer Team)
2016-02-29: Security Acknowledgements (Yahoo Security Incident Team)
2016-03-07: Public Disclosure (Vulnerability Laboratory)

Discovery Status:

Affected Product(s):

Exploitation Technique:

Severity Level:

Technical Details & Description:
Remote attackers are able to spoof the sender name of yahoo email users to send a spoofed sender with spoofed content.
After investigation in the vulnerability we discovered that it is located in the yahoo classic web application product.
Attackers are able to perform the malicious interaction via the yahoo classic mail service. The vulnerability is located
in the `compose message` module of the web service. The request method to inject or intercept as reply is POST.

Affected Module(s):
[+] Message compose [yahoo classic version]

Affected Parameter(s):
[+] from addresses [sender name]

Proof of Concept (PoC):
The vulnerability can be exploited by remote attackers without privileged web-application user account or user interaction.
For security demonstration or to reproduce the web vulnerability follow the provided information and steps below to continue.

Manual steps to reproduce the vulnerability ...
1. Login to attacker email address . change the mod of yahoo to classic one
2. Attacker intercept the sending data and change the parameter [from address 'send name '] to any desired name like " yahoo security "
3. User receives a message as from yahoo security spoofing sender name
4. Successful reproduce of the vulnerability!

PoC: Video

Solution - Fix & Patch:
The fix can be made by disallowing users to change or to edit the sender names in the main POST/GET method requests at all.

Security Risk:
The security risk of the spoofing web vulnerability in the yahoo classic service is estimated as medium. (CVSS 3.0)

Credits & Authors:
Vulnerability Laboratory [Research Team] - Lawrence Amer - http://www.vulnerability-lab.com/show.php?user=Lawrence%20Amer

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