What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-26 · updated 2026-10-26
• Weakness: CWE-601

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.

Affected products

• nosduco nforwardauth: before 1.5.1

References

• https://github.com/nosduco/nforwardauth/commit/664f2602f9e1459558d1c4c55019f6d48bc64c43
• https://github.com/nosduco/nforwardauth/pull/71
• https://github.com/nosduco/nforwardauth/releases/tag/v1.5.1
• https://github.com/nosduco/nforwardauth/security/advisories/GHSA-q64r-v7j5-6hfg

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