What is CVE-2020-5207?

CVE-2020-5207 is a medium-severity vulnerability in Jetbrains Ktor, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.4/10. Published 2020-01-27.

How severe is CVE-2020-5207?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Vulnerability in Jetbrains Ktor

CVE-2020-5207

In Ktor before 1.3.0, request smuggling is possible when running behind a proxy that doesn't handle Content-Length and Transfer-Encoding properly or doesn't handle \n as a headers separator.

Vulnerability class: HTTP Request Smuggling

Published 2020-01-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.008 (54.6th percentile), scored 2026-10-20.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 54.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Jetbrains Ktor
Ktor.io Ktor — versions < 1.3.0

Weakness classification (CWE)

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

References

github.com/ktorio/ktor/security/advisories/GHSA-xrr9-rh8p-433v (Third Party Advisory)
github.com/ktorio/ktor/pull/1547 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2020-5207?: CVE-2020-5207 is a medium-severity vulnerability in Jetbrains Ktor, classified under Inconsistent Interpretation of HTTP Requests (HTTP Request/Response Smuggling). CVSS score: 5.4/10. Published 2020-01-27.
How severe is CVE-2020-5207?: Medium severity. CVSS v3 base score is 5.4 out of 10.