---
id: "CVE-2026-116748"
kind: "vulnerability"
aliases: ["CVE-2026-116748"]
title: "Transmission: permissive CORS lets web pages drive the torrent RPC API"
severity: "high"
cvss: 8.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["linux", "macos", "package", "self-hosted", "torrent-clients", "transmission", "windows"]
not_affected_if: ["rpc-not-reachable-from-browsers", "versions-4.1.3-or-later"]
published_at: "2026-10-26T22:16:59+00:00"
first_seen_at: "2026-10-26T22:25:34+00:00"
updated_at: "2026-10-26T22:27:32+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116748", "first_seen_at": "2026-10-26T22:25:34+00:00"}]
---

# Transmission: permissive CORS lets web pages drive the torrent RPC API

Transmission 4.0.0 before 4.1.3 returns its X-Transmission-Session-Id anti-CSRF token to any web origin via permissive CORS in rpc-server.cc. A malicious web page can read that token and replay it to run RPC calls, such as executing script-torrent-done hooks, changing the download directory, or deleting torrents and data.

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

## How to check

- Run `transmission-daemon --version` or `transmission-remote --version` and check whether it is below `4.1.3`
- Check whether the RPC interface is reachable from a browser, for example the port set by `rpc-port` (default `9091`) in settings.json
- Check whether `rpc-whitelist-enabled` and `rpc-authentication-required` are set in settings.json

## Fix

- Upgrade Transmission to `4.1.3` or later
- Until upgraded, enable `rpc-authentication-required` and restrict access with `rpc-whitelist` or a firewall

## Timeline

- 2026-10-26T22:25:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-116748

## From the sources

Transmission 4.0.0 before 4.1.3 contains a permissive CORS vulnerability in handle_request() in rpc-server.cc that exposes the X-Transmission-Session-Id anti-CSRF token to any web origin. Malicious web pages can read the token from the 409 handshake response and replay it to issue RPC calls, enabling script-torrent-done execution, download-dir changes, or torrent and data deletion.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_