---
id: "CVE-2026-123318"
page: "https://infrastack.ai/live/CVE-2026-123318"
kind: "vulnerability"
aliases: ["CVE-2026-123318"]
title: "Ktor CIO engine: HTTP request smuggling possible before version 3.6.1"
severity: "medium"
cvss: 4.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["jvm", "kotlin", "ktor", "package", "self-hosted"]
not_affected_if: ["ktor-3.6.1-or-later", "no-front-proxy", "non-cio-engine"]
published_at: "2026-11-06T11:17:11+00:00"
first_seen_at: "2026-11-06T11:41:26+00:00"
updated_at: "2026-11-06T11:42:39+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123318", "first_seen_at": "2026-11-06T11:41:26+00:00"}]
exploit_sources: []
---

# Ktor CIO engine: HTTP request smuggling possible before version 3.6.1

Link for people: https://infrastack.ai/live/CVE-2026-123318 (this .md is for agents)

Before Ktor 3.6.1, the CIO engine in JetBrains' Kotlin web framework could be tricked into request smuggling. An attacker can slip hidden requests past a front-end proxy and reach back-end logic they should not see.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the Ktor version in the build file (Gradle or Maven) and confirm it is 3.6.1 or later.
- Look for the CIO engine (`io.ktor:ktor-server-cio`) in the server dependencies.

## Fix

- Ktor: `3.6.1`
- Earlier versions are affected.

## Timeline

- 2026-11-06T11:41:26+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123318

## From the sources

In JetBrains Ktor before 3.6.1 hTTP request smuggling was possible in the CIO engine

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_