---
id: "CVE-2026-65840"
page: "https://infrastack.ai/live/CVE-2026-65840"
kind: "vulnerability"
aliases: ["CVE-2026-65840"]
title: "Fider: email verification key from one tenant logs into another"
severity: "critical"
cvss: 9.6
epss: null
exploited: false
status: "open"
category: "other"
products: []
ecosystems: []
tags: ["fider", "multi-tenant", "other", "self-hosted"]
not_affected_if: ["patched-0.36.0", "single-host-mode"]
published_at: "2026-11-11T19:17:43+00:00"
first_seen_at: "2026-11-11T19:28:48+00:00"
updated_at: "2026-11-11T19:29:41+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-65840", "first_seen_at": "2026-11-11T19:28:48+00:00"}]
exploit_sources: []
---

# Fider: email verification key from one tenant logs into another

Link for people: https://infrastack.ai/live/CVE-2026-65840 (this .md is for agents)

In Fider's multi-tenant mode, a verification key issued on one tenant can be used to sign in as the same email address on a different tenant. An attacker can take over accounts across tenant boundaries.

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

## How to check

- Check the `HOST_MODE` environment variable; the flaw applies only when it is `multi`.
- Check the installed Fider version; versions before `0.36.0` are affected.

## Fix

- Fider: upgrade to `0.36.0` or later.

## Timeline

- 2026-11-11T19:28:48+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-65840

## Documents

- [advisory] Vendor advisory: github.com https://github.com/getfider/fider/security/advisories/GHSA-vxjw-gv4f-vq58
- [fix] Release notes: github.com https://github.com/getfider/fider/releases/tag/v0.36.0

## From the sources

Fider is a feedback portal for feature requests and suggestions. Prior to version 0.36.0, in multi-tenant mode (HOST_MODE=multi), an attacker can use an email verification key issued by Tenant A to authenticate as the same email address on Tenant B. This completely bypasses tenant isolation and allows unauthorized account takeover across tenants. Single-host deployments (HOST_MODE=single, the default) are NOT affected. This issue has been patched in version 0.36.0.

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