CVE-2026-47825: Spring Cloud Gateway Header Spoofing Vulnerability – Critical Patch Required

Technical summary

The vulnerability stems from insufficient validation of proxy headers in Spring Cloud Gateway's header-forwarding logic. The X-Forwarded-For and Forwarded headers are conventionally used by reverse proxies to preserve the original client IP. However, without proper trust-boundary enforcement, an attacker positioned on the network path or able to send direct requests to the gateway can inject arbitrary header values. The gateway then propagates these untrusted values downstream to backend applications, or uses them in internal routing decisions. The issue manifests differently depending on gateway configuration—specifically when the gateway is configured to trust forwarded headers without proper validation of the proxy chain. Both the WebMVC (Spring MVC) and WebFlux (reactive) implementations are affected, indicating the flaw is in the common gateway core rather than transport-specific code.

Business impact

Organizations relying on Spring Cloud Gateway for API management and microservices orchestration face integrity and access-control risks. If downstream services use the forwarded client IP for authentication, rate-limiting, audit logging, or region-specific access policies, an attacker can bypass these controls by spoofing the headers. This could enable unauthorized access to sensitive endpoints, circumvention of geo-blocking policies, session hijacking, or fraudulent activity masquerading as legitimate internal traffic. The impact scales with the number of backend services that trust the forwarded IP—a common pattern in cloud-native architectures.

Affected systems

Spring Cloud Gateway versions across the 3.1.x through 5.0.x release lines are affected. This includes Spring Cloud Gateway 3.1.x (prior to 3.1.13), 4.1.x (prior to 4.1.13), 4.2.x (prior to 4.2.9), 4.3.x (prior to 4.3.5), and 5.0.x (prior to 5.0.2). Organizations running Spring Boot microservices with Spring Cloud Gateway in active development, production, or hybrid cloud deployments should inventory their gateway versions immediately. The vulnerability is particularly critical for enterprises with multi-tier API architectures where the gateway is the primary entry point for internal and external traffic.

Exploitability

This vulnerability has a CVSS 3.1 score of 8.6 (HIGH) with a network-accessible attack vector, no special privileges required, and no user interaction needed. Exploitation is straightforward: an attacker sends a crafted HTTP request with forged X-Forwarded-For or Forwarded headers directly to the gateway or via any network path. No special tooling or deep knowledge of Spring internals is required—basic HTTP client capabilities suffice. The low attack complexity reflects that the configuration weakness is common in deployments where gateways sit behind load balancers or CDNs, creating a false sense of trust in header values. Exploit proof-of-concepts are likely to emerge quickly, making rapid patching essential.

Remediation

Apply the patched versions immediately: Spring Cloud Gateway 3.1.13 or later, 4.1.13 or later, 4.2.9 or later, 4.3.5 or later, or 5.0.2 or later, depending on your active release line. Patches implement proper validation of proxy headers and enforce strict trust-boundary checks. In the interim, mitigation involves explicitly configuring the gateway to only trust forwarded headers from known, verified proxies (use the RemoteAddressResolver or ProxyHeadersFilter configuration to restrict header sources). Additionally, ensure downstream services do not blindly trust client IP values from gateway-forwarded headers without their own validation; implement header signature or mutual TLS verification if relying on IP-based access controls.

Patch guidance

Verify your current Spring Cloud Gateway version using your build tool (Maven: check pom.xml; Gradle: check build.gradle). If running version 3.1.x, 4.1.x, 4.2.x, 4.3.x, or 5.0.x below the patched thresholds listed above, schedule an immediate update. Test patched versions in a staging environment before deploying to production, paying special attention to any custom proxy header configurations or integrations with third-party WAF or load-balancer solutions. The patch is non-breaking for standard configurations; however, organizations with highly customized gateway filter chains should verify compatibility with their extensions. For long-term support (LTS) considerations, consult the Spring Cloud release calendar to understand which versions receive extended support.

Detection guidance

Monitor gateway logs for suspicious X-Forwarded-For and Forwarded header patterns, such as IPs that don't match expected proxy networks or rapid changes in reported source IPs from the same connection. Implement egress monitoring to detect downstream services receiving requests with mismatched source IP claims (compare the header values against actual network flows). Network-based detection can identify requests where the HTTP header claims an internal or trusted IP but the actual source is external. Consider correlation with authentication and access-control logs to identify attempted privilege escalation or policy bypasses. Patch application logs to redact or flag suspicious forwarded headers during the transition period.

Why prioritize this

The combination of ease of exploitation, high CVSS score (8.6), broad applicability across active Spring Cloud Gateway versions, and direct impact on network security controls (IP-based access) makes this a critical priority. The vulnerability requires only network access and no authentication, and it directly undermines trust boundaries in microservices architectures. Organizations should treat this as a P1 remediation task, particularly those with internet-facing APIs or reliance on IP-based rate-limiting or geo-fencing.

Risk score, explained

The CVSS 3.1 score of 8.6 reflects a HIGH-severity network-accessible vulnerability with high integrity impact (I:H). The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N indicates: network-accessible attack vector, low attack complexity, no privilege or user interaction required, and scope change (affecting resources beyond the vulnerable component). The confidentiality impact is none (the header spoofing itself does not leak secrets), but integrity is significantly compromised—downstream trust is broken. The scope-change metric reflects that the vulnerability affects not just the gateway but the broader ecosystem of backend services relying on its trust assertions.

Frequently asked questions