CVE-2026-81509

nforwardauth: Unvalidated r parameter allows post-authentication open redirect

Published Oct 26, 2026 CVSS 3.1 · 6.1 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Nosduco
Nosduco nforwardauth
Vendors & Products Nosduco
Nosduco nforwardauth
Type Values Removed Values Added
Title Unvalidated r parameter allows post-authentication open redirect nforwardauth: Unvalidated r parameter allows post-authentication open redirect
Type Values Removed Values Added
Description 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.
Title Unvalidated r parameter allows post-authentication open redirect
Weaknesses CWE-601
References
Metrics cvssV3_1

{'score': 6.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Oct 26, 2026, 7:34 PM
Reserved
Aug 26, 2026, 8:58 PM
Status
Deferred
Published
Oct 26, 2026, 6:18 PM
Modified
Oct 26, 2026, 8:18 PM