Attack Chain

1. Initial Access (CVE-2026-40976 - Authentication Bypass): An attacker sends a crafted HTTP request to a vulnerable Spring Boot application endpoint.
2. Exploit Default Configuration: If the application is servlet-based, relies on the default Spring Security filter chain, depends on spring-boot-actuator-autoconfigure, and does not depend on spring-boot-health, the default web security configuration fails to enforce authorization.
3. Unauthorized Access: Due to the authorization bypass, the attacker gains unauthorized access to all application endpoints without proper authentication.
4. Session Hijacking (CVE-2026-40973): A local attacker exploits the vulnerability to take control of the ApplicationTemp directory.
5. Code Execution (CVE-2026-40973): Once in control of the ApplicationTemp directory, the attacker can potentially execute arbitrary code within the context of the application.
6. Timing Attack (CVE-2026-40972): An attacker on the same network conducts a timing attack against the DevTools remote secret.
7. Remote Code Execution (CVE-2026-40972): By successfully exploiting the timing attack, the attacker can potentially achieve remote code execution on the vulnerable server.
8. Impact: The attacker gains full control of the system, allowing for data exfiltration, system compromise, and operational downtime.

Impact

Successful exploitation of these Spring Boot vulnerabilities can lead to significant damage, including unauthorized access to sensitive data, complete system compromise, and extended operational downtime. The potential number of victims is vast, considering the widespread use of Spring Boot in various sectors including finance, healthcare, and e-commerce. If an attacker successfully exploits these vulnerabilities, they could steal sensitive customer data, disrupt critical business operations, or deploy ransomware, resulting in significant financial losses and reputational damage.

Recommendation

• Immediately patch Spring Boot applications to the latest versions (>=4.0.6, >=3.5.14, >=3.4.16, >=3.3.19, >=2.7.33) to address CVE-2026-40976, CVE-2026-40973, and CVE-2026-40972.
• Deploy the Sigma rule “Detect Suspicious Access to Actuator Endpoints” to identify potential exploitation attempts targeting CVE-2026-40976 by monitoring access to sensitive actuator endpoints.
• Upscale monitoring and detection capabilities to identify any related suspicious activity as recommended by the CCB.
• Investigate and remediate any potentially compromised systems following the patching process.