Cybersecurity researchers have discovered multiple critical flaws in Amazon Web Services (AWS) offerings that, if successfully exploited, could result in serious consequences.
“The impact of these vulnerabilities range between remote code execution (RCE), full-service user takeover (which might provide powerful administrative access), manipulation of AI modules, exposing sensitive data, data exfiltration and denial of service,” cloud security firm Aqua said in a detailed report shared with The Hacker News.
Following responsible disclosure in February 2024, Amazon addressed the shortcomings over several months from March to June. The findings were presented at Black Hat USA 2024.
Central to the issue, dubbed Bucket Monopoly, is an attack vector referred to as Shadow Resource, which, in this case, refers to the automatic creation of an AWS S3 bucket when using services like CloudFormation, Glue, EMR, SageMaker, ServiceCatalog, and CodeStar.
The S3 bucket name created in this manner is both unique and follows a predefined naming convention (“cf-templates-{Hash}-{Region}”). An attacker could take advantage of this behavior to set up buckets in unused AWS regions and wait for a legitimate AWS customer to use one of the susceptible services to gain covert access to the contents of the S3 bucket.
Based on the permissions granted to the adversary-controlled S3 bucket, the approach could be used to escalate to trigger a DoS condition, or execute code, manipulate or steal data, and even gain full control over the victim account without the user’s knowledge.
To maximize their chances of success, using Bucket Monopoly, attackers can create unclaimed buckets in advance in all available regions and store malicious code in the bucket. When the targeted organization enables one of the vulnerable services in a new region for the first time, the malicious code will be unknowingly executed, potentially resulting in the creation of an admin user that can grant control to the attackers.
However, it’s important to consider that the attacker will have to wait for the victim to deploy a new CloudFormation stack in a new region for the first time to successfully launch the attack. Modifying the CloudFormation template file in the S3 bucket to create a rogue admin user also depends on whether the victim account has permission to manage IAM roles.
Aqua said it found five other AWS services that rely on a similar naming methodology for the S3 buckets – {Service Prefix}-{AWS Account ID}-{Region} – thereby exposing them to Shadow Resource attacks and ultimately permitting a threat actor to escalate privileges and perform malicious actions, including DoS, information disclosure, data manipulation, and arbitrary code execution –
The company also noted that AWS account IDs should be considered a secret, contrary to what Amazon states in its documentation, as they could be used to stage similar attacks.
“This attack vector affects not only AWS services but also many open-source projects used by organizations to deploy resources in their AWS environments,” Aqua said. “Many open-source projects create S3 buckets automatically as part of their functionality or instruct their users to deploy S3 buckets.”
“Instead of using predictable or static identifiers in the bucket name, it is advisable to generate a unique hash or a random identifier for each region and account, incorporating this value into the S3 bucket name. This approach helps protect against attackers claiming your bucket prematurely.”
