HackerRank is a technical hiring platform that helps businesses evaluate software developers based on skill. I found several its website can be attacked to read arbitrary files.
Most websites of Hackerrank use Ruby on Rails (RoR) as their backend. Unfortunately, its recent versions are vulnerable to a file content disclosure vulnerability (CVE-2019-5418). By using path traversal in Accept field of HTTP Request, we can read arbitrary files in remote servers.
I found that two websites of Hackerrank are affected by this flaw including https.www.hackerrank.com and codepair.hackerrank.com.
I just got
/etc/passwd as a PoC. However, according to another research, we can perform a remote code execution attack by combining CVE-2019-5418 and CVE-2019-5420.
Apr 26, 2019 - I contacted the support team to establish a secure channel with the security team
Apr 30, 2019 - The CTO of Hackerrank responded and I provided details
Apr 30, 2019 - Hackerrank team confirmed the vulnerability.
May 13, 2019 - Hackerrank responded that the flaw has been completely fixed and can be disclosed. No bounty was offered, but a t-shirt may come.
May 30, 2019 - The t-shirt is delivered.