A researcher says Yahoo has finally patched a SSRF vulnerability which affected all its services that required images to be processed.
SSRF (Server-Side Request Forgery) vulnerabilities, also known as XSPA (Cross-Site Port Attack), exist when an application that processes user supplied URLs doesn’t properly verify the response from the server before sending it back to the client. An attacker can exploit such flaws to attempt to bypass access controls (e.g. firewalls), conduct port scanning by using the affected servers as a proxy, and even access data on a system.
California-based security researcher Behrouz Sadeghipour says he discovered a SSRF/XSPA vulnerability in a Yahoo image processing system back in July 2014. He immediately reported his findings, but it took the company until June 2015 to address the bug.
Yahoo services such as Flickr and Yahoo Groups allow users to utilize the IMG tag in comments and messages. When posted, the images are processed through yimg.com, Yahoo’s image domain.
The researcher first discovered that he could use the request to yimg.com to execute cross-site scripting (XSS) payloads. He also found that he could launch SSRF attacks by replacing the value of the “url” parameter in the request with his own URL.
Sadeghipour told SecurityWeek that this medium severity vulnerability allowed him to internally access local networks and determine which ports are open on a specific local or remote machine.
The expert has published a blog post containing additional technical information on the bug, along with a video that shows how the vulnerability could have been exploited on Yahoo Groups.
In 2012, researchers at ERPScan published a detailed analysis on the impact of SSRF on business critical applications. Such flaws were also analyzed by Riyaz Ahemed Walikar later in 2012.
In the same year, Walikar identified a SSRF/XSPA vulnerability in the Yahoo! Developer Network. The security bug could have been exploited by an attacker to port scan Internet-facing servers using Yahoo’s machines, the expert said.
Last year, security researcher Andrea Santese reported finding a SSRF/XSPA vulnerability on a domain used at the time by Yahoo for submitting websites to the Yahoo! Directory.
