Mega: Bug bounty program resulted in seven vulnerabilities fixed so far

Crypographic challenges unsolved, no critical remote code execution flaw reported so far, Mega's creators say

By Lucian Constantin, IDG News Service |  Security

One week after launching a security bug bounty program, the new file-storage and sharing service Mega claims to have fixed seven vulnerabilities, none of which met its highest severity classification.

Since Mega was launched three weeks ago, security researchers pinpointed several security issues with the service, ranging from simple cross-site scripting flaws to alleged weaknesses in its cryptographic model.

Mega's creators dismissed some of the issues as theoretical and asked for practical exploits. To support such efforts, a week ago they launched a vulnerability reward program similar to those run by companies such as Google, Facebook, Mozilla and PayPal, as well as two crypto cracking challenges to prove that their cryptographic implementation is solid.

The company promised rewards of up to ¬10,000 for responsibly reported vulnerabilities that meet the program's qualification requirements. In a new blog post published Saturday, the company said that reported vulnerabilities will be ranked according to severity, with "class I" being the least severe and "class VI" being the most severe.

So far, seven vulnerabilities have been reported and fixed, according to the blog post.

Of those, the most severe vulnerability was an "invalid application of CBC-MAC as a secure hash to integrity-check active content loaded from the distributed static content cluster." This vulnerability was rated class IV, which is assigned to "cryptographic design flaws that can be exploited only after compromising server infrastructure (live or post-mortem)."

However, this flaw's description matches that of a vulnerability publicly disclosed by a hacker group called fail0verflow on Jan. 23, over a week before Mega set up its vulnerability reward program. At the time the group reported that Mega was using CBC-MAC -- a message authentication code (MAC) algorithm -- with a fixed key to verify the integrity of JavaScript content served from its secondary servers. The group noted at the time that CBC-MAC was unsuitable for this purpose.

Shortly after fail0verflow's report, security researchers from antivirus firm Sophos reported that Mega dropped CBC-MAC in favor of SHA-256, a proper hashing function. In its new blog post Mega notes that that flaw was fixed within hours.

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