CVE-2021-21369: Potential DoS in Besu HTTP JSON-RPC API

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.7% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-03-09 · updated 2026-06-17
Weakness: CWE-400

Description

Hyperledger Besu is an open-source, MainNet compatible, Ethereum client written in Java. In Besu before version 1.5.1 there is a denial-of-service vulnerability involving the HTTP JSON-RPC API service. If username and password authentication is enabled for the HTTP JSON-RPC API service, then prior to making any requests to an API endpoint the requestor must use the login endpoint to obtain a JSON web token (JWT) using their credentials. A single user can readily overload the login endpoint with invalid requests (incorrect password). As the supplied password is checked for validity on the main vertx event loop and takes a relatively long time this can cause the processing of other valid requests to fail. A valid username is required for this vulnerability to be exposed. This has been fixed in version 1.5.1.

Affected products

hyperledger besu: before 1.5.1 — fixed in 1.5.1

How to fix

Upgrade to a fixed version: hyperledger besu 1.5.1. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2021-21369 or the next vulnerability affects your stack