CVE-2026-49252: Critical Prototype Pollution in @deepstream/server (CVSS 9.9)

Vulnerability Overview

CVE-2026-49252 is a critical prototype pollution vulnerability (CWE-1321, CVSS 9.9) in the @deepstream/server npm package. Prototype pollution occurs when an attacker can inject or overwrite properties on JavaScript's Object.prototype, causing those properties to propagate across all objects in the process. In this case, crafted deepstream protocol messages can be used to manipulate the server's JavaScript object prototypes at runtime.

The impact is severe: successful exploitation within the Node.js server process can lead to remote code execution, privilege escalation, or denial of service — all without requiring authenticated access, depending on deployment posture.

Affected Software

The vulnerability affects the npm package @deepstream/server in all versions prior to 10.0.5. Organisations running deepstream as a real-time data layer — common in financial, gaming, and collaborative SaaS stacks — should treat this as a priority upgrade. No patched release date has been confirmed at the time of writing.

Exploitation Status

A public proof-of-concept (PoC) exploit has been disclosed. This elevates risk significantly: while no in-the-wild exploitation has been confirmed at time of publication, a public PoC dramatically lowers the bar for opportunistic attackers. Defenders should assume weaponisation is imminent and act accordingly — patch or isolate exposed instances now rather than waiting for confirmed active exploitation.

Detection Coverage

Our detection package for CVE-2026-49252 ships query logic across seven SIEM platforms:

• Microsoft Sentinel (KQL) — correlates anomalous deepstream connection events with downstream Node.js process behaviour indicative of prototype chain manipulation.
• Splunk (SPL) — hunts for suspicious message payloads and process telemetry patterns consistent with prototype pollution attempts against deepstream listeners.
• Elastic (EQL) — sequences network ingress events with host-side JavaScript runtime anomalies to surface exploitation chains.
• IBM QRadar (AQL) — aggregates flow and log data to flag deepstream traffic containing prototype-targeting payload patterns.
• Sumo Logic — leverages log search queries targeting deepstream server logs for malformed or oversized message structures.
• Google Chronicle (YARAL) — applies rule-based matching against UDM events for deepstream communication anomalies.
• CrowdStrike (CQL) — detects post-exploitation process behaviour and lateral movement indicators following a successful prototype pollution event in the Node.js process space.

The core detection logic centres on identifying malformed or oversized deepstream protocol messages — particularly those containing __proto__, constructor, or prototype key patterns — combined with downstream behavioural signals such as unexpected child process spawning or privilege changes within the Node.js runtime.

Recommended Action

Upgrade @deepstream/server to version 10.0.5 or later immediately. If patching is not immediately possible, consider network-layer controls to restrict which clients can reach deepstream endpoints, and deploy the detections below to maintain visibility.

Full detection queries, playbooks, and atomic test cases for CVE-2026-49252 are available on the CVE-2026-49252 detection page.