# CVE-2026-123318: JetBrains Ktor HTTP request smuggling in CIO engine

Source: https://junglewise.ai/threats/cve-2026-123318-in-jetbrains-ktor-before-3-6-1-http-request-smuggling-was  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-06. Updated: 2026-11-06  
License: CC BY 4.0 with a link back

CVE-2026-123318 · Severity: medium · CVSS 4.8 · Published 2026-11-06

JetBrains Ktor is a framework for building web applications and APIs. HTTP request smuggling in the CIO engine could allow an attacker to bypass security filters or inject malicious requests that are processed by the server, potentially leading to data exposure or unauthorized actions.

Technologies: [Jetbrains Ktor](https://junglewise.ai/threats/technologies/ktor). Vendors: [Jetbrains](https://junglewise.ai/threats/vendors/jetbrains).

## Quick answers

**Is CVE-2026-123318 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123318 being exploited in the wild.

**How severe is CVE-2026-123318?** Medium severity, with a CVSS score of 4.8, published 6 November 2026.

**Which products and versions are affected?** Jetbrains Ktor before 3.6.1.

**Is there a fix for CVE-2026-123318?** Yes: fixed in 3.6.1. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123318 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-123318?** Check whether you run Jetbrains Ktor at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in 3.6.1

## Technical details

HTTP request smuggling vulnerability exists in the CIO (Coroutine I/O) engine of JetBrains Ktor versions before 3.6.1. The vulnerability allows an attacker to craft ambiguous HTTP requests that are interpreted differently by the proxy/WAF and the backend server, leading to request smuggling. This requires network access and no authentication.

## Affected products

- JetBrains Ktor before 3.6.1

## Timeline

- 2026-11-06: disclosed

## References

- [https://www.jetbrains.com/privacy-security/issues-fixed/](https://www.jetbrains.com/privacy-security/issues-fixed/)

## Related threats

- [JetBrains Ktor session forgery in encrypted cookies](https://junglewise.ai/threats/cve-2026-123317-in-jetbrains-ktor-before-3-6-1-session-forgery-was-possible-via)
- [JetBrains Ktor denial of service in WebSocket decompression](https://junglewise.ai/threats/cve-2026-68762-jetbrains-ktor-denial-of-service-in-websocket-decompression)