CVE-2024-32980 in spin
Summary
by MITRE • 05/08/2024
Spin is the developer tool for building and running serverless applications powered by WebAssembly. Prior to 2.4.3, some specifically configured Spin applications that use `self` requests without a specified URL authority can be induced to make requests to arbitrary hosts via the `Host` HTTP header. The following conditions need to be met for an application to be vulnerable: 1. The environment Spin is deployed in routes requests to the Spin runtime based on the request URL instead of the `Host` header, and leaves the `Host` header set to its original value; 2. The Spin application's component handling the incoming request is configured with an `allow_outbound_hosts` list containing `"self"`; and 3. In reaction to an incoming request, the component makes an outbound request whose URL doesn't include the hostname/port. Spin 2.4.3 has been released to fix this issue.
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Analysis
by VulDB Data Team • 05/08/2024
This vulnerability in Spin represents a sophisticated HTTP header manipulation issue that could enable unauthorized external communications from serverless applications. The flaw exists in the handling of outbound requests where applications configured with the "self" host allowance can be coerced into making requests to arbitrary destinations through manipulation of the Host header. This represents a significant bypass of intended network isolation controls that are fundamental to secure serverless application deployment models. The vulnerability specifically targets the interaction between Spin's runtime routing mechanisms and outbound request processing, creating an unexpected pathway for network egress that was not accounted for in the security model.
The technical implementation of this vulnerability relies on a specific configuration pattern that combines three critical elements. First, the runtime environment must be configured in a way that routes requests based on URL path rather than Host header values while preserving the original Host header. This creates a scenario where the Host header becomes a manipulable parameter for outbound requests. Second, the application component must be explicitly configured with "self" in its allow_outbound_hosts list, which should normally restrict outbound communications to the same host. Third, the component must make outbound requests without including explicit hostname information in the URL, allowing the Host header to be interpreted as the target host. This combination creates a path where an attacker can manipulate the Host header to redirect outbound requests to unintended destinations.
The operational impact of this vulnerability extends beyond simple network egress control bypass. It represents a potential information disclosure risk where malicious actors could exfiltrate data from applications by directing outbound requests to attacker-controlled servers. The vulnerability also opens possibilities for internal network reconnaissance, as applications might be induced to make requests to internal services that would normally be restricted. From an ATT&CK perspective, this maps to techniques involving command and control communications and lateral movement through compromised applications. The vulnerability affects the principle of least privilege in network access controls, potentially allowing applications to communicate with hosts outside their intended scope without proper authorization.
Security mitigations for this vulnerability primarily focus on updating to Spin version 2.4.3 which addresses the core issue by properly handling outbound request routing. Organizations should also review their application configurations to ensure that allow_outbound_hosts lists are properly constrained and avoid using "self" when not strictly necessary. Network segmentation and monitoring should be implemented to detect unusual outbound traffic patterns that might indicate exploitation attempts. The fix implemented in version 2.4.3 likely involves stricter validation of outbound request URLs and ensures that the Host header is not used to influence the target host when explicit URL information is available. This vulnerability highlights the importance of proper input validation and the potential security implications of HTTP header manipulation in serverless environments, aligning with CWE categories related to improper input validation and insecure direct object references. Organizations should conduct thorough security assessments of their Spin-based applications to ensure proper configuration and avoid the vulnerable combinations of runtime routing and application configuration patterns.