CVE-2026-41840: Spring WebFlux Multipart DoS Vulnerability – Patch Guide

Technical summary

CVE-2026-41840 is a resource exhaustion vulnerability in Spring WebFlux's multipart request handling. The vulnerability stems from improper resource management (CWE-401) when processing multipart form data, allowing an attacker to craft requests that consume excessive server resources and trigger a denial of service condition. The attack does not require authentication, network privileges, or user interaction, though it does require some degree of attack complexity to exploit effectively. The vulnerability affects Spring Framework versions 5.3.0–5.3.48, 6.1.0–6.1.27, 6.2.0–6.2.18, and 7.0.0–7.0.7.

Business impact

Availability impact is the primary concern. Successful exploitation can render Spring WebFlux applications unresponsive, disrupting dependent services and end-user access. The moderate CVSS score reflects the availability-only risk; confidentiality and integrity are not compromised. For mission-critical microservices architectures, even brief service interruptions can cascade across multiple dependent systems. Organizations relying on Spring-based APIs for core business operations should prioritize patching to minimize operational risk.

Affected systems

VMware Spring Framework versions spanning four major/minor release lines are affected: 5.3.x (up to 5.3.48), 6.1.x (up to 6.1.27), 6.2.x (up to 6.2.18), and 7.0.x (up to 7.0.7). Any application using Spring WebFlux (Spring's reactive web framework) within these versions and accepting multipart requests—such as file upload endpoints—is vulnerable. Organizations must audit their dependency trees to identify affected Spring Framework versions, regardless of whether applications explicitly depend on Spring WebFlux or inherit it transitively.

Exploitability

The attack is network-accessible and requires no authentication or user interaction, lowering the barrier to exploitation. However, the moderate attack complexity suggests the attacker must craft requests with specific characteristics to trigger the resource exhaustion. The vulnerability is not yet in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild has not been confirmed as of the last update. Nevertheless, the straightforward attack vector (HTTP multipart requests) means exploitation capability could be developed or discovered quickly once the vulnerability details are widely publicized.

Remediation

Upgrade Spring Framework to a patched version immediately. For each affected line: 5.3.x users should update to 5.3.49 or later, 6.1.x to 6.1.28 or later, 6.2.x to 6.2.19 or later, and 7.0.x to 7.0.8 or later. Verify the exact patch version against VMware's official Spring Framework security advisory to ensure you are applying the correct fix. If immediate patching is not feasible, disable or restrict multipart request handling on exposed endpoints as a temporary mitigation. Review network access controls to limit which clients can reach affected endpoints.

Patch guidance

Begin by inventorying applications and their Spring Framework dependencies using build tools (Maven, Gradle) to identify those within affected version ranges. Prioritize patching production systems first, followed by development and staging environments. Test patches in a staging environment to verify compatibility with your application before deploying to production. Monitor Spring Framework release notes and VMware security advisories for any patch supersessions or additional guidance. Consider implementing automated dependency scanning in your CI/CD pipeline to prevent future use of vulnerable Spring Framework versions.

Detection guidance

Monitor application logs for unusual spikes in multipart request processing, resource consumption, or error rates that correlate with incoming HTTP requests. Network intrusion detection systems can flag suspicious patterns of multipart requests, particularly those with abnormal headers, payload sizes, or repetition rates targeting file-upload or form-processing endpoints. Endpoint monitoring should track CPU and memory usage of Java processes running Spring WebFlux applications; DoS attacks typically manifest as sustained elevation in resource consumption. Correlate application performance monitoring (APM) data with access logs to identify whether elevated resource usage coincides with specific client IP addresses or request patterns.

Why prioritize this

This vulnerability warrants near-term action despite its medium CVSS score because of the breadth of affected versions, the ubiquity of Spring Framework in enterprise Java ecosystems, and the availability impact. The unauthenticated, network-accessible nature of the attack combined with the lack of user-interaction requirements makes it operationally significant. Organizations with public-facing or internal microservices built on Spring WebFlux should prioritize patching ahead of less-accessible vulnerabilities. The four affected release lines mean even legacy applications on 5.3.x may require attention, complicating patch management.

Risk score, explained

The CVSS 3.1 score of 5.9 (MEDIUM) reflects availability impact as the primary risk (high impact on availability) paired with moderate attack complexity and no impact on confidentiality or integrity. The score appropriately captures that while an attacker can disrupt service, they cannot steal data or modify system behavior. However, context matters: for critical services, availability impact alone justifies urgent patching. The moderate attack complexity suggests non-trivial exploitation but does not eliminate the threat, especially as proof-of-concept code or exploitation techniques become public.

Frequently asked questions