CVE-2026-40969: VMware Spring gRPC Information Disclosure

CVE-2026-40969 Overview

CVE-2026-40969 is an information disclosure vulnerability in VMware Spring gRPC that exposes raw AuthenticationException messages to unauthenticated remote callers through gRPC status descriptions. This vulnerability allows attackers to obtain detailed information about authentication failures, which can be leveraged for reconnaissance and further targeted attacks against the affected system.

Critical Impact
Unauthenticated attackers can gather sensitive authentication error details that reveal internal security mechanisms, potentially aiding in credential enumeration, brute force optimization, or identifying misconfigured authentication providers.

Affected Products

VMware Spring gRPC versions 1.0.0 through 1.0.2
Older, unsupported versions of Spring gRPC

Discovery Timeline

2026-04-28 - CVE-2026-40969 published to NVD
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-40969

Vulnerability Analysis

This vulnerability falls under CWE-209: Generation of Error Message Containing Sensitive Information. The core issue is that Spring gRPC's error handling mechanism does not sanitize or redact the content of AuthenticationException messages before transmitting them back to the client in the gRPC status description field.

When an authentication failure occurs on the server side, the full exception message—which may contain details about the authentication mechanism, user existence, credential validity, or backend system information—is directly included in the gRPC response. This behavior violates the security principle of providing minimal error information to unauthenticated users.

Root Cause

The root cause stems from improper exception handling in Spring gRPC's authentication interceptor or security filter chain. When an AuthenticationException is thrown during the gRPC request processing pipeline, the framework captures the exception and populates the gRPC Status.UNAUTHENTICATED response with the raw exception message rather than a generic, non-revealing error message.

This design flaw allows internal error details that should remain server-side to leak to external callers, regardless of whether they have successfully authenticated.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

Sending gRPC requests to an affected Spring gRPC endpoint with invalid, malformed, or missing authentication credentials
Analyzing the returned gRPC status description for detailed error messages
Using the disclosed information to enumerate valid usernames, identify authentication backend types, or refine attack strategies

The vulnerability can be triggered by simply initiating authentication attempts against exposed gRPC services. The detailed error responses can reveal information such as whether a user account exists, what type of authentication provider is in use, or specific validation failures that occurred during the authentication process.

Detection Methods for CVE-2026-40969

Indicators of Compromise

Unusual volume of failed authentication attempts from single source IPs
Sequential or enumerated username patterns in gRPC authentication requests
Clients making repeated requests with slight variations in authentication parameters
Evidence of credential stuffing or brute force activity following reconnaissance patterns

Detection Strategies

Monitor gRPC server logs for repeated UNAUTHENTICATED status responses to the same client
Implement rate limiting on authentication endpoints to detect and throttle enumeration attempts
Deploy network monitoring to identify unusual patterns in gRPC traffic targeting authentication services
Review application logs for patterns indicating systematic testing of authentication mechanisms

Monitoring Recommendations

Enable verbose logging for authentication failures and correlate with client IP addresses
Set up alerts for authentication failure rate thresholds that may indicate active exploitation
Monitor for reconnaissance patterns where attackers probe multiple usernames or authentication variations
Implement security information and event management (SIEM) rules to detect credential enumeration behaviors

How to Mitigate CVE-2026-40969

Immediate Actions Required

Upgrade Spring gRPC to version 1.0.3 or later immediately
Review gRPC endpoints for public exposure and restrict access where possible
Implement network-level controls to limit access to gRPC services
Enable enhanced authentication logging to detect potential exploitation attempts

Patch Information

VMware has released Spring gRPC version 1.0.3 which addresses this vulnerability by sanitizing authentication exception messages before including them in gRPC status descriptions. Organizations should upgrade to this version or later to remediate the issue. Detailed patch information is available in the Spring Security Advisory for CVE-2026-40969.

Workarounds

Implement a custom gRPC interceptor that catches AuthenticationException instances and returns generic error messages
Deploy a reverse proxy or API gateway that sanitizes error responses before they reach external clients
Configure network segmentation to limit direct access to gRPC services from untrusted networks
Implement application-level exception handlers that override default Spring gRPC error message behavior

bash

# Configuration example - Update Spring gRPC dependency in Maven pom.xml
# Upgrade from vulnerable versions (1.0.0-1.0.2) to fixed version 1.0.3

# In your pom.xml, update the spring-grpc dependency:
# <dependency>
#     <groupId>org.springframework.grpc</groupId>
#     <artifactId>spring-grpc</artifactId>
#     <version>1.0.3</version>
# </dependency>

# After updating, rebuild and redeploy your application:
mvn clean package