---
id: "CVE-2026-123317"
page: "https://infrastack.ai/live/CVE-2026-123317"
kind: "vulnerability"
aliases: ["CVE-2026-123317"]
title: "Ktor: tampered encrypted session cookies let attackers forge sessions"
severity: "high"
cvss: 8.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["jvm", "kotlin", "ktor", "package", "session-cookies"]
not_affected_if: ["no-session-cookies", "version-3.6.1-or-later"]
published_at: "2026-11-06T11:17:11+00:00"
first_seen_at: "2026-11-06T11:41:26+00:00"
updated_at: "2026-11-06T11:41:54+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123317", "first_seen_at": "2026-11-06T11:41:26+00:00"}]
exploit_sources: []
---

# Ktor: tampered encrypted session cookies let attackers forge sessions

Link for people: https://infrastack.ai/live/CVE-2026-123317 (this .md is for agents)

Ktor versions before 3.6.1 accept tampered encrypted session cookies, so an attacker can forge a session. A forged session can act as another user, depending on what the application stores in its sessions.

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

## How to check

- Check the Ktor version in the project's build file (for example `ktor` in `gradle/libs.versions.toml` or `build.gradle.kts`); versions below `3.6.1` are affected.
- Check whether the application uses Ktor's session feature with encrypted cookies (`sessions { cookie(...) }` with an encryption transform).

## Fix

- Ktor: upgrade to `3.6.1` or later

## Timeline

- 2026-11-06T11:41:26+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123317

## From the sources

In JetBrains Ktor before 3.6.1 session forgery was possible via tampered encrypted session cookies

---

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