CVE-2026-40971: Spring Boot Information Disclosure Flaw

CVE-2026-40971 Overview

CVE-2026-40971 is a certificate validation bypass vulnerability affecting Spring Boot's RabbitMQ auto-configuration. When configured to use an SSL bundle, the application fails to perform hostname verification when establishing connections to RabbitMQ brokers, potentially allowing man-in-the-middle attacks on adjacent networks.

Critical Impact

Attackers on the same network segment could intercept and manipulate communications between Spring Boot applications and RabbitMQ brokers by presenting fraudulent certificates, potentially leading to data interception or message tampering.

Affected Products

• Spring Boot 4.0.0 through 4.0.5 (fixed in 4.0.6)
• Spring Boot 3.5.0 through 3.5.13 (fixed in 3.5.14)

Discovery Timeline

• 2026-04-27 - CVE-2026-40971 published to NVD
• 2026-04-28 - Last updated in NVD database

Technical Details for CVE-2026-40971

Vulnerability Analysis

This vulnerability is classified under CWE-295 (Improper Certificate Validation). The flaw resides in Spring Boot's RabbitMQ auto-configuration module when SSL bundles are utilized for securing broker connections. While the SSL/TLS handshake itself completes successfully, the implementation omits the critical step of verifying that the certificate's hostname matches the target RabbitMQ broker's hostname.

This missing verification step means that an attacker who can obtain any valid certificate (even one issued for a completely different domain) could potentially impersonate the RabbitMQ broker. The vulnerability requires the attacker to have adjacent network access, which limits but does not eliminate the exploitation risk in enterprise environments where network segmentation may not be strictly enforced.

Root Cause

The root cause of CVE-2026-40971 stems from Spring Boot's SSL bundle configuration not enabling hostname verification by default when establishing AMQP connections to RabbitMQ. The auto-configuration logic validates that a certificate is properly signed and trusted but does not confirm that the certificate was issued for the specific hostname being connected to. This is a common oversight in TLS implementations where developers focus on encryption and trust chain validation while neglecting the hostname binding check.

Attack Vector

The vulnerability requires an adjacent network position (AV:A), meaning the attacker must be on the same network segment as the target application or RabbitMQ broker. The attack complexity is high (AC:H) as it requires specific conditions to be met:

1. The attacker must position themselves to intercept network traffic between the Spring Boot application and RabbitMQ broker
2. The attacker needs a valid TLS certificate (potentially for any domain)
3. ARP spoofing, DNS poisoning, or similar techniques may be required to redirect traffic

A successful attack could allow interception of sensitive message queue data, modification of messages in transit, or credential theft if authentication tokens are passed through the message broker.

Detection Methods for CVE-2026-40971

Indicators of Compromise

• Unexpected certificate warnings or changes in SSL/TLS negotiation logs from RabbitMQ connections
• ARP table anomalies or unexpected MAC address associations on network segments hosting Spring Boot applications
• DNS resolution inconsistencies for RabbitMQ broker hostnames
• Unusual network latency patterns indicative of traffic interception

Detection Strategies

• Monitor Spring Boot application logs for SSL handshake failures or certificate-related warnings
• Implement network traffic analysis to detect potential ARP spoofing or DNS poisoning attempts
• Review SSL/TLS connection logs on RabbitMQ brokers for connections from unexpected certificate subjects
• Deploy intrusion detection systems with rules for detecting man-in-the-middle attack patterns

Monitoring Recommendations

• Enable detailed SSL/TLS logging in Spring Boot applications to capture certificate chain details
• Implement certificate pinning monitoring to detect when unexpected certificates are presented
• Configure network monitoring tools to alert on unusual traffic patterns between application servers and RabbitMQ brokers
• Establish baseline metrics for RabbitMQ connection establishment times to detect interception delays

How to Mitigate CVE-2026-40971

Immediate Actions Required

• Upgrade Spring Boot 4.0.x installations to version 4.0.6 or later
• Upgrade Spring Boot 3.5.x installations to version 3.5.14 or later
• Review all applications using SSL bundles with RabbitMQ auto-configuration for potential exposure
• Implement network segmentation to limit adjacent network attack surface

Patch Information

VMware/Pivotal has released security patches addressing this hostname verification issue. The fixes are available in Spring Boot 4.0.6 and 3.5.14. The patches enable proper hostname verification by default when SSL bundles are configured for RabbitMQ connections. For detailed information, refer to the Spring Security Advisory CVE-2026-40971.

Workarounds

• Implement strict network segmentation between Spring Boot applications and RabbitMQ brokers to limit adjacent network access
• Configure mutual TLS (mTLS) authentication to require client certificates, adding an additional layer of verification
• Use VPN or encrypted tunnels between application servers and RabbitMQ brokers as an additional protection layer
• Implement certificate pinning at the application level if upgrading is not immediately possible

If immediate patching is not feasible, organizations should consider implementing custom SSL context configuration that explicitly enables hostname verification. Consult the Spring Security Advisory for specific configuration guidance until patches can be applied.