Security Experts:

Misconfigured Jenkins Servers Leak Sensitive Data

A researcher has conducted an analysis of Jenkins servers and found that many of them leak sensitive information, including ones belonging to high-profile companies.

London-based researcher Mikail Tunç used the Shodan search engine to find Jenkins servers accessible from the Internet and discovered roughly 25,000 instances.

The expert analyzed approximately half of them and determined that 10-20% were misconfigured. He spent weeks manually validating the issues he discovered and notifying affected vendors.

Jenkins is an open source automation server used by software developers for continuous integration and delivery. Since the product is typically linked to a code repository such as GitHub and a cloud environment such as AWS or Azure, failure to configure the application correctly can pose a serious security risk.

Some of the misconfigured systems discovered by Tunç provided guest or administrator permissions by default, while others allowed guest or admin access to anyone who registered an account. Some Jenkins servers used a SAML/OAuth authentication system linked to Github or Bitbucket, but they allowed any GitHub or Bitbucket account to log in rather than just accounts owned by the organization.

Tunc said a vast majority of the misconfigured Jenkins servers leaked some type of sensitive information, including credentials for private source code repositories, credentials for deployment environments (e.g. usernames, passwords, private keys and AWS tokens), and job log files that included credentials and other sensitive data.

One of the exposed Jenkins instances, which leaked sensitive tokens, belonged to Google, but the tech giant quickly addressed the issue after being informed via its bug bounty program.

The researcher also named several major UK-based companies, including Transport for London, supermarkets Sainsbury’s and Tesco, credit checking company ClearScore, educational publisher Pearson, and newspaper publisher News UK. Some of these companies allegedly exposed highly sensitive data, but Tunç said he often had difficulties in responsibly disclosing his findings.

“I want to make it absolutely clear that I did not exploit any vulnerabilities to gain access to Jenkins servers – I simply walked through the front door which was visible to the world, then told the owners to close said front door,” the researcher noted in a blog post.

While Tunç received products, vouchers and thanks for his work from the companies he alerted, misconfigured Jenkins instances can be highly problematic and some vendors have paid significant bug bounties for such security holes.

A few months ago, two researchers reported earning a total of $20,000 from Snapchat after finding exposed Jenkins instances that allowed arbitrary code execution and access to sensitive data.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.