CVE-2026-19484: fastify fastify\/busyboy Infinite Loop

Vulnerability summary

CVE-2026-19484 is a high (CVSS 7.5) Infinite Loop vulnerability in fastify fastify\/busyboy. EPSS estimates a 0.61% chance of exploitation in the next 30 days, higher than 48.4% of scored vulnerabilities.

Timeline

1. 13-08-2026
   PublishedVulnerability first disclosed.
2. 13-08-2026
   Last modifiedVulnerability information updated.

Description

@fastify/busboy is a multipart form-data parser. In versions 3.1.0 through 3.2.0, a remote unauthenticated attacker can stall the Node.js event loop by sending a multipart request whose boundary is crafted to a specific length. The vendored streaming search stores its skip table in a fixed 256 entry byte array, and a boundary of exactly 252 bytes makes the search needle 256 bytes, which truncates the default skip distance to zero and turns the search into a CPU bound loop on a small body. A single small request can keep one core busy and deny service to other requests handled by the same process. The issue is fixed in @fastify/busboy 3.2.1, which widens the skip table so the skip distance is preserved. Users should upgrade to 3.2.1.

• CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.
• CWE-1322Use of Blocking Code in Single-threaded, Non-blocking ContextThe product uses a non-blocking model that relies on a single threaded process for features such as scalability, but it contains code that can block when it is invoked.