CVE
Fider: Cross-Tenant Authentication Bypass via Missing tenant_id Filter in getVerificationByKey
Only affects Fider in multi-tenant mode (HOST_MODE=multi) before 0.36.0. Fixed in 0.36.0.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 0.36.0
- Who is exposed
- Specific setups only
Do first: Check whether your setup matches what the bug needs. Multi-tenant mode (HOST_MODE=multi) is enabled
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 18/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Fider, a feedback portal, has a flaw in its multi-tenant mode that lets an attacker use an email verification key from one tenant to sign in as the same email address on another tenant, bypassing tenant isolation. The attack can be carried out remotely by someone who has a low-privilege login, and no user action is needed.
Read the original description
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.
Who should check
Operators of self-hosted Fider (getfider/fider) below 0.36.0 running HOST_MODE=multi with multiple tenants on one instance
Read the source excerpt
“In multi-tenant mode ( HOST_MODE=multi ), an attacker can use an email verification key”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure8/25Specific setups only, reachable over the network
- Reach?/20Unknown. No tracked technology or package matched
- Severity9.6/10CVSS 9.6
- No patch0/5No signal
What would change the score
- Would score about 68 if added to CISA KEV
- Would score about 63 if CISA's SSVC rates exploitation active
- Would score about 25 if CISA's SSVC rates it automatable
What to do
Check whether your setup matches what the bug needs.
Multi-tenant mode (HOST_MODE=multi) is enabledUpgrade to a fixed version: 0.36.0.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-65840 (Fider: Cross-Tenant Authentication Bypass via Missing tenant_id Filter in getVerificationByKey), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-65840 (entry last updated 2026-11-11):
Affected:
- getfider fider: fixed in 0.36.0
Fixed versions: 0.36.0.
Conditions (all must be true for the bug to be hit):
- Multi-tenant mode (HOST_MODE=multi) is enabled (source: https://github.com/getfider/fider/security/advisories/GHSA-vxjw-gv4f-vq58)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, low-privilege login, no user action.
CISA KEV: CVE-2026-65840 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-65840 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/getfider/fider/security/advisories/GHSA-vxjw-gv4f-vq58
- https://github.com/getfider/fider/releases/tag/v0.36.0
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-65840
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-65840"}.Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- getfider fider
fixed in 0.36.0
Evidence 4
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 1
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-65840
Is CVE-2026-65840 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
An email verification key issued for one tenant can be used on another tenant to sign in as the same email address. This bypasses tenant isolation, so accounts on other tenants can be taken over, including administrator accounts.Source: github.com
Which versions are affected by CVE-2026-65840?
fider: before 0.36.0.Source: cve.now feed data
Am I affected, and how do I check?
The issue applies to Fider versions before 0.36.0 that run in multi-tenant mode, where HOST_MODE is set to multi. To check, look at the HOST_MODE setting in the deployment configuration and the installed Fider version.Source: github.com
How do I fix CVE-2026-65840?
Upgrade Fider to version 0.36.0, which contains the fix (commit ce4f44bb).Source: github.com