CVE-2026-18209

MEDIUMNVD 4.74.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.7 under NVD CVSS v3. EPSS exploit probability: 0.2%, top 91% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
4.7EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 4.7Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

CVSS v3
4.7
EG Score
4.7(medium)
EG Risk
21(Track)
EG Risk 21/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity47% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
9%
KEV
Not listed

Published

July 31, 2026

Last Modified

August 7, 2026

Advisory Details (2)

Auto-updated Aug 7, 2026
Patch available. Sources: redhat.
redhat

2508305 – (CVE-2026-18209) CVE-2026-18209 keycloak-services: keycloak-services: OIDC redirect_uri fragment bypass in HTTP parameter pollution check

https://bugzilla.redhat.com/show_bug.cgi?id=2508305
redhat Patch Available

CVE-2026-18209 - Red Hat Customer Portal

Affected: Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to a

https://access.redhat.com/security/cve/CVE-2026-18209

Vendor Advisories for CVE-2026-18209(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 19× in last 7d / 57× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. 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. Most recent first.

  1. 2026-08-20 22:55 UTCEPSS rescore
  2. 2026-08-20 14:56 UTCEG score recompute
  3. 2026-08-20 14:55 UTCGHSA enrichment
  4. 2026-08-19 17:03 UTCEPSS rescore
  5. 2026-08-19 16:43 UTCGHSA enrichment
  6. 2026-08-18 18:26 UTCEG score recompute
  7. 2026-08-18 18:26 UTCGHSA enrichment
  8. 2026-08-18 13:48 UTCEPSS rescore
  9. 2026-08-17 19:40 UTCEG score recompute
  10. 2026-08-17 19:40 UTCGHSA enrichment
  11. 2026-08-17 13:47 UTCEPSS rescore
  12. 2026-08-16 20:35 UTCEG score recompute
  13. 2026-08-16 20:35 UTCGHSA enrichment
  14. 2026-08-16 14:56 UTCEPSS rescore
  15. 2026-08-16 02:14 UTCEPSS rescore
  16. 2026-08-15 22:24 UTCEG score recompute
  17. 2026-08-15 22:24 UTCGHSA enrichment
  18. 2026-08-15 01:30 UTCEPSS rescore
  19. 2026-08-15 00:13 UTCGHSA enrichment
  20. 2026-08-14 02:02 UTCEG score recompute
  21. 2026-08-14 02:02 UTCGHSA enrichment
  22. 2026-08-13 22:00 UTCEPSS rescore
  23. 2026-08-13 03:52 UTCEG score recompute
  24. 2026-08-13 03:52 UTCGHSA enrichment
  25. 2026-08-12 13:50 UTCEPSS rescore
Show 32 more
  1. 2026-08-12 05:41 UTCEG score recompute
  2. 2026-08-12 05:41 UTCGHSA enrichment
  3. 2026-08-11 13:42 UTCEPSS rescore
  4. 2026-08-11 07:30 UTCEG score recompute
  5. 2026-08-11 07:30 UTCGHSA enrichment
  6. 2026-08-11 00:00 UTCEPSS rescore
  7. 2026-08-10 09:19 UTCEG score recompute
  8. 2026-08-10 09:19 UTCGHSA enrichment
  9. 2026-08-09 13:46 UTCEPSS rescore
  10. 2026-08-09 11:09 UTCEG score recompute
  11. 2026-08-09 11:09 UTCGHSA enrichment
  12. 2026-08-08 16:37 UTCEPSS rescore
  13. 2026-08-08 12:58 UTCEG score recompute
  14. 2026-08-08 12:58 UTCGHSA enrichment
  15. 2026-08-07 14:46 UTCEG score recompute▲ 1.30
  16. 2026-08-07 14:46 UTCGHSA enrichment
  17. 2026-08-07 14:46 UTCNVD updateCVSS v3 → 4.7 · severity → MEDIUM
  18. 2026-08-06 23:18 UTCEG score recompute
  19. 2026-08-06 23:18 UTCGHSA enrichment
  20. 2026-08-06 13:46 UTCEPSS rescore
  21. 2026-08-05 19:17 UTCEPSS rescore
  22. 2026-08-04 15:10 UTCEPSS rescore
  23. 2026-08-03 16:56 UTCEG score recompute
  24. 2026-08-03 16:56 UTCGHSA enrichment
  25. 2026-08-03 10:35 UTCEPSS rescore
  26. 2026-08-02 02:26 UTCEPSS rescore
  27. 2026-08-01 04:15 UTCEPSS rescore
  28. 2026-07-31 16:23 UTCEG score recompute
  29. 2026-07-31 16:23 UTCGHSA enrichment
  30. 2026-07-31 08:18 UTCEG score recompute
  31. 2026-07-31 07:28 UTCEG score recompute
  32. 2026-07-31 07:28 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-18209?
CVE-2026-18209 is a medium vulnerability published on July 31, 2026. A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion.…
When was CVE-2026-18209 disclosed?
CVE-2026-18209 was first published in the National Vulnerability Database on July 31, 2026, with the most recent update on August 7, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-18209 actively exploited?
CVE-2026-18209 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 90.7% of all scored CVEs.
What is the CVSS score of CVE-2026-18209?
CVE-2026-18209 has a CVSS v3 base score of 4.7 (NVD).
How do I remediate CVE-2026-18209?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-18209, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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