CVE-2026-1527CWE-93

undici is vulnerable to CRLF Injection via upgrade option

Medium · published March 12, 2026

CVSS v3.1
4.6
EPSS
0%
Percentile
19.5
In the wild
Unconfirmed
What it is

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`

}

The record
Technical detail
CVSS v3.1
4.6 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
CVSS v4.0
Not supplied
EPSS
0.00281 · 19.5th percentile
Weakness
CWE-93 · Improper Neutralization of CRLF Sequences ('CRLF Injection')
Published
2026-03-12T20:17Z
EPSS history
Timeline
  • 12 MAR 20:17Z
    undici is vulnerable to CRLF Injection via upgrade option
    cvelistv5