CVE-2026-81509

MEDIUMPre-NVD 6.16.1
EchelonGraph scoreLOW confidence

This medium-severity CVE scores 6.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3% (24th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: a secondary CVSS source
Trending — 4 sources updated this week

Also known asEUVD-2026-110037 (ENISA EUVD)Source: ENISA EUVD

6.1EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 6.1Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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.

CVSS v3
6.1
EG Score
6.1MEDIUMlow confidence
EG Risk
27
EG Risk 27/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity61% × 45%
Impact severity (EG Severity): CVSS 6.1 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0% × 40%
No KEV listing, EG-KEV tier or EPSS when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
24th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (6.1): severity, escalated by confirmed exploitation. This CVE's 6.1 is its impact severity (EG Severity), not escalated.

EG Severity
6.1 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS. FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

October 26, 2026

Last Modified

October 26, 2026

Advisory Details (4)

Auto-updated Oct 26, 2026
🔬 Proof of concept available. Patch available. Sources: github, github_pr, github_commit, github_release.
GitHub release Patch Available

v1.5.1

Patch available: nosduco/nforwardauth v1.5.1

https://github.com/nosduco/nforwardauth/releases/tag/v1.5.1
GitHub commit Patch Available

commit 664f2602f9e1 (nosduco/nforwardauth)

Patch available: nosduco/nforwardauth v1.5.1 (contains commit 664f2602f9e1)

https://github.com/nosduco/nforwardauth/commit/664f2602f9e1459558d1c4c55019f6d48bc64c43
GitHub pull request Patch Available

fix: CVE-601 vulnerabiilty. scope redirect uris to cookie domain

Patch available: nosduco/nforwardauth v1.5.1 (PR #71 merged 2026-07-10)

https://github.com/nosduco/nforwardauth/pull/71
GitHub advisoryMentions a patch (unverified)🟡 PoC Available

Unvalidated r parameter allows post-authentication open redirect · Advisory · nosduco/nforwardauth · GitHub

https://github.com/nosduco/nforwardauth/security/advisories/GHSA-q64r-v7j5-6hfg

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 12× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-11-01 16:35 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  2. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  3. 2026-10-30 16:35 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  4. 2026-10-29 16:34 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  5. 2026-10-28 16:33 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  6. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  7. 2026-10-26 20:35 UTCEG score recompute
  8. 2026-10-26 19:49 UTCEG score recompute
  9. 2026-10-26 19:03 UTCEG score recompute
  10. 2026-10-26 18:01 UTCENISA EUVD ID recordedEUVD-2026-110037 · Source: ENISA EUVD
  11. 2026-10-26 17:38 UTCEG score recomputeFirst assessed: 6.1 MEDIUM
  12. 2026-10-26 17:35 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-81509?
CVE-2026-81509 is a medium-severity vulnerability; its CVE record was published on October 26, 2026. 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…
When was the CVE record for CVE-2026-81509 published?
The CVE record for CVE-2026-81509 was published on October 26, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 26, 2026; the record at its source may have been updated since.
Is CVE-2026-81509 actively exploited?
CVE-2026-81509 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (24th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-81509?
CVE-2026-81509 has a CVSS base score of 6.1 (a secondary CVSS source that NVD displays; NVD's own analysis pending). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-81509?
A fix for CVE-2026-81509 is available: update to the fixed version the vendor names in its advisory.

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