Microsoft has quietly started notifying some Azure customers that a serious security vulnerability in the Azure App Service has caused the exposure of hundreds of source code repositories.
Microsoft’s confirmation comes more than two months after it was reported by Israeli cloud security startup Wiz and weeks after Redmond quietly patched the flaw and released notifications to “a limited subset of customers” believed to be at risk.
In an advisory, the Microsoft Security Response Center described the flaw as an issue where customers can unintentionally configure the .git folder to be created in the content root, which would put them at risk for information disclosure.
“This, when combined with an application configured to serve static content, makes it possible for others to download files not intended to be public. We have notified the limited subset of customers that we believe are at risk due to this and we will continue to work with our customers on securing their applications,” Microsoft said.
The company warned that App Service Linux customers who deployed applications using Local Git after files were created or modified in the content root directory are impacted.
“The combination of the .git folder in the content folder along with the application which serves out static content makes the app susceptible to source code exposure,” Redmond added.
A separate technical note from the Wiz research team describes the flaw as an insecure default behavior in the Azure App Service that exposed the source code of customer applications written in PHP, Python, Ruby, or Node, that were deployed using “Local Git”.
“The vulnerability, which we dubbed as “NotLegit”, has existed since September 2017 and has probably been exploited in the wild,” the company warned.
The Wiz researchers described exploitation as “extremely easy” and noted that there are signs that unknown malicious actors are already launching exploits.
“To assess the chance of exposure with the issue we found, we deployed a vulnerable Azure App Service application, linked it to an unused domain, and waited patiently to see if anyone tried to reach the .git files. Within 4 days of deploying, we were not surprised to see multiple requests for the .git folder from unknown actors,” the company said.
“As this exploitation method is extremely easy, common, and is actively being exploited, we encourage all affected users to overview their application’s source code and evaluate the potential risk,” Wiz added.
Researchers at the Israel-based Wiz have been actively finding and documenting gaping security holes — ChaosDB and OMIGOD are two examples — in Microsoft’s flagship Azure cloud computing infrastructure.