What is CVE-2021-22959?

CVE-2021-22959 is a medium-severity vulnerability in Llhttp, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 6.5/10. Published 2021-11-15.

How severe is CVE-2021-22959?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Llhttp

CVE-2021-22959

The parser in accepts requests with a space (SP) right after the header name before the colon. This can lead to HTTP Request Smuggling (HRS) in llhttp < v2.1.4 and < v6.0.6.

Vulnerability class: HTTP Request Smuggling

Published 2021-11-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.032 (87.5th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 87th percentile — 87.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.029 · newest: 0.032 · change: +0.002

Affected products

Llhttp
Node.js Node — versions 4.0, 5.0, 6.0
Oracle Graalvm — versions 20.3.4, 21.3.0
Debian Linux — versions 11.0

Weakness classification (CWE)

CWE-444 — Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling)

References

hackerone.com/reports/1238709 (Exploit, Third Party Advisory, Issue Tracking)
www.oracle.com/security-alerts/cpujan2022.html (Patch, Third Party Advisory)
www.debian.org/security/2022/dsa-5170 (vendor-advisory, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2021-22959?: CVE-2021-22959 is a medium-severity vulnerability in Llhttp, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 6.5/10. Published 2021-11-15.
How severe is CVE-2021-22959?: Medium severity. CVSS v3 base score is 6.5 out of 10.