Executive Summary

This vulnerability is a pre-authentication denial of service issue in certain versions of React Server Components. It occurs because the software unsafely deserializes payloads from HTTP requests to Server Function endpoints, which can trigger an infinite loop that hangs the server process and stops it from handling further requests.

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Mitigation Strategies

To mitigate this vulnerability, immediately upgrade React Server Components packages to fixed versions 19.0.2, 19.1.3, or 19.2.2. Users who updated for the prior critical vulnerability must update again, as earlier patches remain vulnerable. The fix prevents unsafe deserialization that causes infinite loops and denial of service. Additionally, coordinate with hosting providers for any temporary mitigations if applicable. [1]

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Detection Guidance

Detection involves monitoring for unusual server behavior such as infinite loops or server hangs caused by crafted HTTP requests to Server Function endpoints. Specific commands are not provided in the resources, but network monitoring tools could be used to detect repeated or malformed HTTP requests targeting these endpoints. Additionally, checking server logs for repeated deserialization errors or high CPU usage may indicate exploitation attempts. [1]

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Mitigation Strategies

The immediate mitigation step is to upgrade React Server Components packages to fixed versions 19.0.2, 19.1.3, or 19.2.2. Users who updated for the prior critical vulnerability must update again, as earlier patches remain vulnerable. Temporary mitigations were coordinated with hosting providers, but the React team strongly recommends immediate package upgrades to prevent exploitation. [1]

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Impact Analysis

The impact of this vulnerability is that an attacker can cause the server to hang indefinitely by sending specially crafted requests, leading to a denial of service where legitimate users cannot access the server or its services.

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