React Server Components Security: CVE-2025-55184 & CVE-2025-55183
Understanding, Mitigating, and Detecting CVE-2025-55184 & CVE-2025-55183
Dec 13, 2025, 15:00
The recent React2Shell disclosure (CVE-2025-55182) was swiftly followed by community research that uncovered additional weaknesses in React Server Components (RSC). Two such vulnerabilities—CVE-2025-55184 (Denial of Service) and CVE-2025-55183 (Source Code Exposure)—illustrate the broader security implications of unsafe deserialization in the RSC Flight protocol and similar runtime paths. These discoveries, and their subsequent patch updates (including CVE-2025-67779, an incomplete patch follow-up), underscore persistent risks in modern full-stack JavaScript and server-rendered frameworks.
This analysis will deepen your understanding of these CVEs, explain their operational risks, contextualize them within real-world attack activity, and provide practical mitigation and detection recommendations—not just summarizing the Vercel bulletin, but elevating it for developers and security practitioners.
Why These CVEs Matter
React Server Components (RSC) represent a paradigm shift in how modern web frameworks handle server-side rendering and data fetching, blending client and server logic. RSC’s Flight protocol enables the server to serialize structured UI and logic data back to the client, but this convenience comes at a cost: unsafe deserialization paths create exploitable attack surfaces.
What Has Happened So Far
A high-impact unauthenticated Remote Code Execution vulnerability (CVE-2025-55182) was disclosed. It allows an attacker to execute arbitrary code via malicious deserialized HTTP requests on default configurations.
2. Follow-on Weaknesses Discovered
Shortly after, researchers found additional issues in adjacent code:
●CVE-2025-55184: High severity Denial of Service via infinite loops in deserialization.
●CVE-2025-55183: Medium severity Source Code Exposure allowing attackers to leak backend Server Function code.
3. Incomplete Patches and Subsequent CVE
Initial patches for the DoS issue were insufficient, leading to CVE-2025-67779. This emphasizes the risk inherent in patching unsafe deserialization logic without comprehensive threat modeling.
Technical Impact Breakdown
CVE-2025-55184 — Denial of Service (High Severity)
This vulnerability exists in the deserialization logic used by RSC. A malicious HTTP request can cause the server to enter an infinite loop or hung state, consuming CPU and rendering the service unresponsive.
●Impact: Service availability degradation or outage.
●Exploit Vector: Unauthenticated HTTP request triggering a faulty deserialization path.
●Severity: High (CVSS 7.5).
While not permitting code execution, availability attacks can have severe business impacts—downtime during peak usage, customer churn, SLA breaches, and operational costs from manual remediation.
CVE-2025-55183 — Source Code Exposure (Medium Severity)
This vulnerability allows an attacker to coerce the server into returning stringified source code of RSC Server Functions. The danger lies in the unintended exposure of proprietary logic or hardcoded secrets within the code base:
●Impact: Intellectual property leakage; potential exposure of hardcoded credentials.
●Attack Requirements: A vulnerable Server Function present in the application’s code.
●Severity: Medium.
This is particularly concerning in environments where business logic or secret material is not adequately segmented, audited, or obfuscated.
Real-World Exploitation and Activity
Although CVE-2025-55184 and CVE-2025-55183 do not enable Remote Code Execution, they follow an exploited family of vulnerabilities including React2Shell. Monitoring shows that:
●Threat actors—both opportunistic and state-linked—are actively scanning for and leveraging RSC-related RCE vulnerabilities in CVE-2025-55182.
●Even vulnerabilities that do not provide shell access (like DoS and source code leaks) are attractive for adversaries aiming to degrade service, fingerprint backend logic, or leverage downtime as part of multi-stage campaigns.
●Early exploitation trends highlight the risk of patch delays and the need for rigorous dependency and runtime scanning.
Upgrade and Patch Management Strategy
The mainline remediation is straightforward: upgrade React and Next.js to patched versions listed in the React and Vercel advisories:
●React packages: patched to 19.0.3, 19.1.4, 19.2.3 (and equivalents).
●Next.js: upgrade to the versions listed in the Vercel bulletin (e.g., 14.2.35, 15.0.7, up to 16.0.10, etc.).
Best Practices
●Lockfile hygiene: Commit updated lockfiles immediately with version bumps.
●Verify all transitive dependencies: Ensure no outdated RSC packages exist in monorepos or workspaces.
●Continuous scanning: Use Software Composition Analysis (SCA) tools in your CI/CD to detect vulnerable dependencies earlier in the workflow.
Mitigation Beyond Upgrading
Network and Runtime Protections
●Deploy Web Application Firewalls (WAFs) with rules trained to identify malformed RSC payloads.●Rate-limit and monitor deserialization endpoints to detect abnormal traffic patterns.
●Use canary deployments behind feature flags to verify patch effectiveness before full rollout.
Code Hardening
●Avoid hardcoding sensitive keys or tokens in server functions.●Implement defense-in-depth patterns like input validation around any deserialization entry points—not just trusting framework behavior.
Observability and Logging
●Log failed deserialization attempts with anomalous payload sizes or execution time thresholds.●Integrate alerts for spikes in 5xx responses that may indicate DoS attempts early.
Lessons Learned and Long-Term Guidance
These events highlight several key software security insights for teams building on modern web stacks:
1. Unsafe Deserialization is a Systemic Risk
Any framework that accepts structured data from the client for server-side usage (as in RSC’s Flight protocol) requires rigorous validation and sandboxing.
2. Follow-On Vulnerabilities Are Common
Successful exploitation or patching of a critical flaw often leads researchers to adjacent code paths, uncovering additional issues—as seen with CVE-2025-67779. This suggests proactive, comprehensive threat modeling is indispensable.
3. Reliance on Default Configurations Increases Risk
Most developers adopt defaults. However, defaults that expose unsafe deserialization widen the attack surface.
●If your app does not use RSC features, consider disabling them or auditing for their presence explicitly.
