Medium severity · published Mar 12, 2026
CVE-2026-1527
undici is vulnerable to CRLF Injection via upgrade option
4.6
CVSS
0.3%
EPSS
No
On KEV
Description
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`
}
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 20% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
UN
undici · undici
< 6.24.0; 7.0.0 < 7.24.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-1527
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-1527
Vendor Advisory
https://cna.openjsf.org/security-advisories.html
Mitigation
https://github.com/nodejs/undici/security/advisories/GHSA-4992-7rv2-5pvq
Permissions Required
https://hackerone.com/reports/3487198
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