CVE-2026-0621
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk38th percentile - higher than 38% of all known CVEs
Summary
A ReDoS vulnerability in Anthropic's MCP TypeScript SDK up to version 1.25.1 exists in the UriTemplate class when processing RFC 6570 exploded array patterns. The dynamically generated regular expression contains nested quantifiers that can cause catastrophic backtracking on specially crafted inputs, leading to excessive CPU consumption.
Risk Assessment
An attacker can supply a malicious URI that causes the Node.js process to become unresponsive, resulting in a denial of service (DoS) and potential disruption of application availability.
Recommendation
Immediately update the MCP TypeScript SDK to a version later than 1.25.1, which includes a fix for the ReDoS vulnerability.
Other vulnerabilities in MCP TypeScript SDK
See all- CVE-2026-111767High
In MCP TypeScript SDK from version 1.24.0 to before 1.32.0, the experimental tasks feature (taskStore) did not check which session created a task. Clients sharing one InMemoryTaskStore could list, read and cancel each other's tasks.
- CVE-2026-104850High
MCP TypeScript SDK versions from 1.12.0 before 1.31.0 and 2.2.0 let the MCP server a client connects to decide which authorization server receives the client's OAuth credentials. Stored and pre-provisioned credentials were not bound to the authorization server they belong to. A malicious or compromised MCP server could name its own authorization server in its protected resource metadata. Without user interaction, the client would send that server the `refresh_token` and `client_secret` stored from an earlier sign-in (1.x), or the configured `client_secret` or signed assertion of a bundled non-interactive provider (1.x and 2.x). Only applications using the SDK as an MCP client over HTTP with an `authProvider`: your own `OAuthClientProvider`, or the bundled `ClientCredentialsProvider`, `PrivateKeyJwtProvider`, `StaticPrivateKeyJwtProvider` or (2.x) `CrossAppAccessProvider` and that may connect to an MCP server the owners do not fully trust while holding credentials for a legitimate authorization server are affected. `@modelcontextprotocol/sdk` 1.31.0 (1.x) and `@modelcontextprotocol/client` 2.2.0 (2.x) patch the issue. A workaround is available. 2.0.0 and 2.1.0 already accept `expectedIssuer`. On 1.x, the only workaround is to connect OAuth-enabled clients only to trusted MCP servers.
- CVE-2026-25536High
A vulnerability in the MCP TypeScript SDK allows cross-client response data leak when a single server and transport instance is reused across multiple client connections. The issue affects versions 1.10.0 through 1.25.3, most notably in stateless StreamableHTTPServerTransport deployments.
Original NVD description (English source)
Anthropic's MCP TypeScript SDK versions up to and including 1.25.1 contain a regular expression denial of service (ReDoS) vulnerability in the UriTemplate class when processing RFC 6570 exploded array patterns. The dynamically generated regular expression used during URI matching contains nested quantifiers that can trigger catastrophic backtracking on specially crafted inputs, resulting in excessive CPU consumption. An attacker can exploit this by supplying a malicious URI that causes the Node.js process to become unresponsive, leading to a denial of service.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS