CVE-2026-1527

ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an attacker can inject CRLF sequences (\r\n) to: * Inject arbitrary HTTP headers * Terminate the HTTP request prematurely and smuggle raw data to non-HTTP services (Redis, Memcached, Elasticsearch) The vulnerability exists because undici writes the upgrade value directly to the socket without validating for invalid header characters: // lib/dispatcher/client-h1.js:1121 if (upgrade) { header += `connection: upgrade\r\nupgrade: ${upgrade}\r\n` }

Published Mar 12, 2026
CVSS 4.6 medium
0.3% chance of exploitation in the next 30 days (EPSS)
A fix is available

Affected software

undici

In the news

Multiple vulnerabilities in IBM products CERT-FR · Sep 25, 2026

CVE-2026-1527 at the National Vulnerability Database