What’s Vulnerable › Vulnerabilities

CVE-2020-5207: Request smuggling is possible in Ktor when both chunked TE and content length specified

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-01-27 · updated 2026-06-17
• Weakness: CWE-444

Description

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.

Affected products

• JetBrains Ktor: before 1.3.0 — fixed in 1.3.0

How to fix

Upgrade to a fixed version: JetBrains Ktor 1.3.0. Check the vendor advisory for mitigations.

References

• https://github.com/ktorio/ktor/pull/1547
• https://github.com/ktorio/ktor/security/advisories/GHSA-xrr9-rh8p-433v
• https://github.com/ktorio/ktor/pull/1547
• https://github.com/ktorio/ktor/security/advisories/GHSA-xrr9-rh8p-433v

Get alerted when CVE-2020-5207 or the next vulnerability affects your stack