DNS Rebinding Vulnerability in Google APIs Toolkit

CVE-2026-9739

What is CVE-2026-9739?

CVE-2026-9739 is a DNS rebinding vulnerability found in the Google APIs Toolkit, specifically affecting users connecting via Toolbox using Server-Sent Events (SSE) with the version specification v2024-11-05. This vulnerability arises from an oversight in which the Access-Control-Allow-Origin: * header was retained in the SSE initialization handler, despite the implementation of security measures such as allowed-origins and allowed-hosts flags intended to mitigate security risks. This oversight can lead to unauthorized access to sensitive resources and could fundamentally compromise the integrity of applications relying on these APIs.

Organizations utilizing the Google APIs Toolkit may face significant security risks due to this vulnerability, as it opens the door for attackers to exploit cross-domain weaknesses inherent in the DNS resolution process. By successfully executing a DNS rebinding attack, malicious users could perform actions on behalf of authenticated users, making it crucial to address this vulnerability to protect sensitive data and operations.

Potential impact of CVE-2026-9739

1. Unauthorized Data Access: This vulnerability can allow attackers to leverage DNS rebinding to access sensitive user data and functionality that should be protected by same-origin policies. This breach of confidentiality could lead to exposure of personal or proprietary information.

2. Execution of Malicious Commands: Attackers may exploit this vulnerability to inject malicious commands into a target’s session, potentially gaining remote control over affected systems, leading to data manipulation and execution of unauthorized transactions.

3. Increased Risk of System Compromise: Organizations affected by CVE-2026-9739 may experience higher risks of full system compromise as attackers can leverage this vulnerability to escalate privileges and pivot to more secure parts of the network, heightening the overall attack surface and leading to more catastrophic cyber incidents.

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CVE-2026-9739

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