CVE-2021-29480 in Ratpack
Summary
by MITRE • 06/30/2021
Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, the client side session module uses the application startup time as the signing key by default. This means that if an attacker can determine this time, and if encryption is not also used (which is recommended, but is not on by default), the session data could be tampered with by someone with the ability to write cookies. The default configuration is unsuitable for production use as an application restart renders all sessions invalid and is not multi-host compatible, but its use is not actively prevented. As of Ratpack 1.9.0, the default value is a securely randomly generated value, generated at application startup time. As a workaround, supply an alternative signing key, as per the documentation's recommendation.
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Analysis
by VulDB Data Team • 07/04/2021
The vulnerability described in CVE-2021-29480 affects the Ratpack web application toolkit, specifically targeting the client-side session management module. This issue stems from a fundamental flaw in how session signing keys are generated and managed within the framework's default configuration. The vulnerability represents a classic cryptographic weakness where predictable values are used as cryptographic keys, creating opportunities for session manipulation and potential unauthorized access to user sessions. The flaw exists in versions prior to 1.9.0 where the application startup time serves as the default signing key, fundamentally undermining the security of session management.
The technical implementation of this vulnerability lies in the deterministic nature of the signing key generation process. When the application starts, the system uses the exact timestamp of the startup as the basis for generating session signing keys. This approach creates several security concerns that align with CWE-330, which addresses the use of insufficiently random values in cryptographic operations. Attackers who can determine or predict the application startup time can potentially forge session cookies, as the signing key becomes known to unauthorized parties. The vulnerability becomes particularly dangerous when combined with the default configuration that does not enforce encryption, leaving session data exposed to tampering and modification.
The operational impact of this vulnerability extends beyond simple session hijacking to encompass broader security implications for web applications built on the Ratpack framework. When an application restart occurs, all existing sessions become invalid due to the time-based key generation, creating denial of service conditions while simultaneously making session data vulnerable to manipulation. This design flaw also prevents proper multi-host deployment scenarios, as the time-based signing keys would differ across servers, breaking session continuity. The vulnerability's severity is amplified by the fact that the default configuration is unsuitable for production environments, yet the framework does not actively prevent its use, creating a dangerous default state that exposes applications to attack. This aligns with ATT&CK technique T1555.003 which covers credentials from password storage providers and T1078.004 which addresses valid accounts in cloud environments.
The mitigation strategy for this vulnerability requires immediate action to update to Ratpack version 1.9.0 or later, where the framework implements securely random signing key generation at application startup time. This approach addresses the core cryptographic weakness by ensuring that signing keys are unpredictable and cryptographically strong. Organizations should also implement the documented workaround of supplying alternative signing keys, which provides additional security layers beyond the default implementation. The recommended solution directly addresses the root cause by eliminating the deterministic time-based key generation and replacing it with properly randomized cryptographic keys that meet industry standards for session management security. This remediation approach aligns with security best practices outlined in OWASP Top Ten and NIST guidelines for web application security, ensuring that session management components are properly configured for production environments.