A recent report by the security firm Miggo has revealed that over 15,000 applications using Amazon Web Services (AWS) Application Load Balancer (ALB) are at risk due to a critical configuration flaw. Dubbed ALBeast, the attack takes advantage of misconfigured ALB settings, allowing malicious actors to bypass both authentication and authorization. The issue stems from how ALB handles authentication rather than a vulnerability within the ALB itself.
Miggo’s findings highlight that attackers can create their own ALB instance, sign a token they control, and alter the configuration to mimic the victim’s issuer. This forged token can then be used to gain unauthorized access to the victim’s application, potentially leading to data breaches and other security incidents. A Censys search identified over 370,000 internet-exposed instances of AWS ALB, with Miggo estimating that more than 15,000 could be susceptible to this attack. However, even non-internet-facing apps could be targeted if attackers have network access.
AWS was informed of the potential risks in April 2024 and has since updated its documentation and provided new code to help customers mitigate these attacks. The company has also stated that the issue is not an inherent flaw in ALB but a result of misconfiguration by customers. AWS recommends that customers ensure their applications only accept requests from their own ALB, using security groups and following ALB security best practices to prevent ALBeast attacks.
Despite Miggo’s estimates, AWS claims that significantly fewer applications are vulnerable and has proactively contacted affected customers to provide guidance on securing their configurations. As the reliance on cloud services continues to grow, this incident underscores the importance of adhering to security best practices to protect critical business resources from emerging threats.
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