CVE-2015-8748 in Radicale
Summary
by MITRE
Radicale before 1.1 allows remote authenticated users to bypass owner_write and owner_only limitations via regex metacharacters in the user name, as demonstrated by ".*".
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Analysis
by VulDB Data Team • 07/06/2022
The vulnerability identified as CVE-2015-8748 affects Radicale versions prior to 1.1, representing a significant authorization bypass flaw that undermines the security controls designed to protect calendar and contact data. This issue stems from insufficient input validation in the authentication and authorization mechanisms, specifically targeting the owner_write and owner_only access control restrictions that are fundamental to preventing unauthorized data access within the Radicale calendar server implementation.
The technical flaw manifests through improper handling of regular expression metacharacters within user name inputs, where attackers can exploit the regex pattern matching functionality to craft malicious user names that circumvent intended access controls. When an attacker submits a username containing regex metacharacters such as ".*", the system interprets this pattern in a way that grants broader access privileges than intended, effectively allowing unauthorized users to assume ownership or gain write access to resources they should not be permitted to modify. This vulnerability operates at the intersection of improper input validation and insecure regex handling, creating a path for privilege escalation through crafted authentication credentials.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it fundamentally compromises the integrity and confidentiality of calendar and contact data stored within the Radicale server environment. An authenticated attacker who can manipulate their user identity through regex injection can potentially modify or delete sensitive personal information, disrupt calendar synchronization services, and undermine the trust model that users place in the calendar server. This represents a critical failure in the principle of least privilege, where the system fails to properly enforce access controls that should be strictly maintained between different user roles and data ownership boundaries.
Organizations utilizing Radicale servers prior to version 1.1 face significant risk of data compromise and unauthorized modifications to calendar and contact information, particularly in environments where multiple users share the same server instance. The vulnerability's exploitation requires only basic authentication credentials and knowledge of the regex injection technique, making it accessible to attackers with minimal specialized skills. Security teams should consider this issue in the context of broader access control failures and evaluate their overall authentication and authorization frameworks for similar vulnerabilities.
The mitigation strategy involves upgrading to Radicale version 1.1 or later, which includes proper input sanitization and regex handling that prevents malicious patterns from bypassing access controls. Additionally, system administrators should implement comprehensive input validation at all levels of the application stack, particularly for user identification and authentication components. Organizations should also consider implementing additional security controls such as monitoring for unusual access patterns and implementing multi-factor authentication to reduce the impact of credential compromise. This vulnerability aligns with CWE-20, Improper Input Validation, and represents a specific instance of how regex injection can be leveraged for privilege escalation attacks. The ATT&CK framework categorizes this as a privilege escalation technique, specifically through credential manipulation and access control bypass methods that exploit weaknesses in authentication systems.