---
id: "CVE-2026-81509"
kind: "vulnerability"
aliases: ["CVE-2026-81509"]
title: "nforwardauth: login redirect parameter lets attackers send victims to external sites"
severity: "medium"
cvss: 6.1
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["auth", "nforwardauth", "package", "reverse-proxy", "self-hosted"]
not_affected_if: ["version-1.5.1-or-later"]
published_at: "2026-10-26T18:18:46+00:00"
first_seen_at: "2026-10-26T18:31:44+00:00"
updated_at: "2026-10-26T18:34:07+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-81509", "first_seen_at": "2026-10-26T18:31:44+00:00"}]
---

# nforwardauth: login redirect parameter lets attackers send victims to external sites

nforwardauth, a forward auth service, takes an unvalidated r query parameter on /login and redirects to it after login. An attacker can craft a real login link that sends a victim to an attacker-controlled site, enabling phishing that abuses the trusted auth domain.

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

## How to check

- Check the installed nforwardauth version, for example `nforwardauth --version` or the image tag, and see if it is below `1.5.1`
- Search your reverse proxy or service config for the /login route to confirm nforwardauth is deployed

## Fix

- Upgrade nforwardauth to `1.5.1` or later, which contains the patch

## Timeline

- 2026-10-26T18:31:44+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-81509

## From the sources

nforwardauth is a forward auth service that allows the use of a single authentication middleware for multiple sites. Versions prior to 1.5.1 accept an unvalidated `r` query parameter on the `/login` endpoint and use them as the post-authentication redirect destination. An unauthenticated attacker can create a legitimate `nforwardauth` login URL that redirects a victim to an attacker-controlled website after the victim successfully authenticates. This issue may facilitate phishing and other social-engineering attacks by abusing the trust associated with the legitimate authentication domain. This vulnerability does not provide an unauthenticated ForwardAuth bypass. Version 1.5.1 contains a patch.

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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_