Medium · CVSS 6.1CVE-2026-81509

nforwardauth: Unvalidated r parameter allows post-authentication open redirectCVE-2026-81509

Answer in brief

CVE-2026-81509 records a Medium severity (CVSS 6.1) vulnerability in nforwardauth: Unvalidated r parameter allows post-authentication open redirect. The current sources do not mark it as known exploited. The current feed maps nosduco/nforwardauth (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 26, 2026Updated Oct 26, 2026Source checked Oct 26, 2026First seen by HOL Oct 26, 2026Material review Oct 26, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.1
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 6.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps nosduco/nforwardauth (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
nosduco/nforwardauthgeneric	<1.5.1	1.5.1

Recommended response

Check inventory. Check lockfiles and deployed manifests for nosduco/nforwardauth.
Review the reported fix. Update nosduco/nforwardauth to 1.5.1 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 26, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 26, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.