CVE-2026-1527
Severity CVSS v4.0:
Pending analysis
Type:
CWE-93
Improper Neutralization of CRLF Sequences ('CRLF Injection')
Publication date:
12/03/2026
Last modified:
12/03/2026
Description
ImpactWhen an application passes user-controlled input to the upgrade option of client.request(), an attacker can inject CRLF sequences (\r\n) to:<br />
<br />
* Inject arbitrary HTTP headers<br />
* Terminate the HTTP request prematurely and smuggle raw data to non-HTTP services (Redis, Memcached, Elasticsearch)<br />
The vulnerability exists because undici writes the upgrade value directly to the socket without validating for invalid header characters:<br />
<br />
// lib/dispatcher/client-h1.js:1121<br />
if (upgrade) {<br />
header += `connection: upgrade\r\nupgrade: ${upgrade}\r\n`<br />
}
Impact
Base Score 3.x
4.60
Severity 3.x
MEDIUM