Race Condition Affecting @modelcontextprotocol/sdk package, versions >=1.10.0 <1.26.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published5 Feb 2026
- disclosed4 Feb 2026
- creditArpeet Kale, Eli M
Introduced: 4 Feb 2026
CVE-2026-25536 (opens in a new tab)How to fix?
Upgrade @modelcontextprotocol/sdk to version 1.26.0 or higher.
Overview
@modelcontextprotocol/sdk is a Model Context Protocol implementation for TypeScript
Affected versions of this package are vulnerable to Race Condition via the reuse of a single McpServer or Server instance and transport across multiple concurrent client connections. An attacker can access response data intended for other clients by exploiting JSON-RPC message ID collisions, which causes responses to be misrouted between clients.
Note:
This is only exploitable if a server instance is shared across concurrent client sessions and clients generate overlapping message IDs.
Workaround
This vulnerability can be mitigated by creating fresh McpServer and transport instances for each request (in stateless mode) or for each session (in stateful mode).