CVE-2026-47837: Spring Cloud Config Auth Bypass Vulnerability

CVE-2026-47837 Overview

CVE-2026-47837 is a missing authentication vulnerability [CWE-306] in Spring Cloud Config Server. The /monitor endpoint accepts webhook requests without validating their origin or authenticity. An attacker with network access can send crafted webhook payloads to trigger configuration refresh events. This affects Spring Cloud Config versions 5.0.0 through 5.0.4, 4.3.0 through 4.3.4, 4.0.0 through 4.2.8, and all releases through 3.1.14. The flaw impacts the availability of downstream services that subscribe to config-refresh notifications.

Critical Impact
Unauthenticated network-adjacent attackers can send unvalidated webhook requests to the /monitor endpoint, disrupting availability of Spring Cloud-managed services.

Affected Products

Spring Cloud Config 5.0.0 through 5.0.4
Spring Cloud Config 4.0.0 through 4.3.4
Spring Cloud Config through 3.1.14

Discovery Timeline

2026-08-26 - CVE-2026-47837 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-47837

Vulnerability Analysis

Spring Cloud Config Server exposes the /monitor endpoint to receive webhook notifications from source-control providers such as GitHub, GitLab, Bitbucket, and Gitea. When a webhook arrives, the server parses the payload, extracts changed file paths, and publishes a RefreshRemoteApplicationEvent to connected clients through Spring Cloud Bus. The endpoint does not validate webhook signatures or require authentication.

Any actor able to reach the endpoint over the network can submit forged payloads. Repeated invocations force cascading configuration refreshes across every subscribed application, exhausting resources and degrading service availability. The scope changes because the impact extends beyond the Config Server to downstream microservices that consume its refresh events.

Root Cause

The root cause is missing authentication for a critical function [CWE-306]. The /monitor handler trusts inbound HTTP requests based solely on payload shape rather than verifying an HMAC signature, shared secret, or authenticated identity. Deployments that place Config Server behind a network boundary but omit endpoint-level authentication remain exposed to any tenant sharing that network.

Attack Vector

The attack vector is network-based and requires no user interaction. An attacker sends an HTTP POST request to /monitor with a JSON body matching a supported provider format. The Config Server processes the request and emits refresh events to bus-connected clients. Sustained request volume produces a denial-of-service condition across the connected application fleet.

See the Spring Security Advisory CVE-2026-47837 for vendor technical details.

Detection Methods for CVE-2026-47837

Indicators of Compromise

Unexpected HTTP POST requests to the /monitor path on Spring Cloud Config Server instances from unknown source addresses.
Elevated rates of RefreshRemoteApplicationEvent messages on Spring Cloud Bus that do not correlate with legitimate commits.
Downstream services logging repeated configuration reloads or bean re-initialization events.

Detection Strategies

Inspect Config Server access logs for /monitor requests lacking expected upstream source IPs or missing provider-specific headers such as X-GitHub-Event or X-Gitlab-Token.
Alert on request bursts to /monitor that exceed baseline webhook traffic volume from source-control providers.
Correlate /monitor requests with subsequent client refresh spikes to identify amplification patterns.

Monitoring Recommendations

Forward Spring Boot Actuator and application logs to a centralized SIEM for real-time query and alerting.
Track availability and CPU metrics on Config Server clients to catch degradation caused by refresh storms.
Monitor egress from Config Server to Spring Cloud Bus brokers for abnormal event throughput.

How to Mitigate CVE-2026-47837

Immediate Actions Required

Upgrade Spring Cloud Config to a patched release above 5.0.4, 4.3.4, 4.2.8, or 3.1.14 as listed in the vendor advisory.
Restrict network access to /monitor so that only source-control provider IP ranges can reach the endpoint.
Enable authentication on all Actuator and management endpoints exposed by Config Server.

Patch Information

Refer to the Spring Security Advisory CVE-2026-47837 for fixed version numbers and upgrade instructions. Apply the vendor patch to close the missing authentication gap at the /monitor handler.

Workarounds

Front the Config Server with a reverse proxy that validates webhook HMAC signatures before forwarding to /monitor.
Disable the spring-cloud-config-monitor dependency if webhook-based refresh is not required in the deployment.
Apply firewall or service-mesh policies that limit /monitor reachability to specific source-control provider CIDR blocks.

bash

# Example NGINX allow-list for /monitor endpoint
location /monitor {
    allow 140.82.112.0/20;   # GitHub webhook range
    allow 192.30.252.0/22;   # GitHub webhook range
    deny all;
    proxy_pass http://config-server-upstream;
}