CVE-2026-18209

MEDIUMNVD 4.74.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.7 under NVD CVSS v3. EPSS exploit probability: 0.4% (32nd percentile of EPSS-scored CVEs). GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
Trending — 4 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: 0.4%CVSS: 4.7Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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
4.7MEDIUMmedium confidence
EG Risk
21
EG Risk 21/100CISA SSVC

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%
CISA SSVC: Track at every mission impact level.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.4%
EPSS %ILE
32nd
KEV
Not listed

CISA SSVCTrack 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). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

July 31, 2026

Last Modified

September 16, 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(3)

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

Patch Availability(2)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatrhbk-openshift-rhel9/rhbk-openshift-rhel92026-09-16redhat
redhatrhbk/keycloak-rhel9-operator:26.6-202026-09-16redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 18× in last 7d / 78× 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.

Showing the most recent 100 of 172 total refreshes for this CVE.

  1. 2026-10-04 23:21 UTCEPSS rescore
  2. 2026-10-04 06:33 UTCEG score recompute
  3. 2026-10-04 06:33 UTCVendor advisory
  4. 2026-10-04 06:33 UTCGHSA enrichment
  5. 2026-10-03 14:25 UTCEPSS rescore
  6. 2026-10-02 16:51 UTCEG score recompute
  7. 2026-10-02 16:51 UTCVendor advisory
  8. 2026-10-02 16:51 UTCGHSA enrichment
  9. 2026-10-01 19:49 UTCEPSS rescore
  10. 2026-10-01 02:48 UTCEG score recompute
  11. 2026-10-01 02:48 UTCVendor advisory
  12. 2026-10-01 02:48 UTCGHSA enrichment
  13. 2026-09-30 15:02 UTCEPSS rescore
  14. 2026-09-29 15:20 UTCEPSS rescore
  15. 2026-09-29 06:50 UTCEG score recompute
  16. 2026-09-29 06:50 UTCVendor advisory
  17. 2026-09-29 06:50 UTCGHSA enrichment
  18. 2026-09-28 13:51 UTCEPSS rescore
  19. 2026-09-27 18:57 UTCEG score recompute
  20. 2026-09-27 18:57 UTCVendor advisory
  21. 2026-09-27 18:57 UTCGHSA enrichment
  22. 2026-09-27 13:47 UTCEPSS rescore
  23. 2026-09-26 15:58 UTCEPSS rescore
  24. 2026-09-25 07:56 UTCEG score recompute
  25. 2026-09-25 07:56 UTCVendor advisory
Show 75 more
  1. 2026-09-25 07:56 UTCGHSA enrichment
  2. 2026-09-24 09:45 UTCEG score recompute
  3. 2026-09-24 09:45 UTCVendor advisory
  4. 2026-09-24 09:45 UTCGHSA enrichment
  5. 2026-09-23 11:35 UTCEG score recompute
  6. 2026-09-23 11:35 UTCVendor advisory
  7. 2026-09-23 11:35 UTCGHSA enrichment
  8. 2026-09-22 13:23 UTCEG score recompute
  9. 2026-09-22 13:23 UTCVendor advisory
  10. 2026-09-22 13:23 UTCGHSA enrichment
  11. 2026-09-19 23:43 UTCEG score recompute
  12. 2026-09-19 23:43 UTCVendor advisory
  13. 2026-09-19 23:43 UTCGHSA enrichment
  14. 2026-09-18 23:28 UTCEG score recompute
  15. 2026-09-18 23:28 UTCVendor advisory
  16. 2026-09-18 23:28 UTCGHSA enrichment
  17. 2026-09-18 19:27 UTCEPSS rescore
  18. 2026-09-18 01:17 UTCEG score recompute
  19. 2026-09-18 01:17 UTCVendor advisory
  20. 2026-09-18 01:17 UTCGHSA enrichment
  21. 2026-09-16 19:20 UTCGHSA enrichment
  22. 2026-09-16 18:53 UTCGHSA enrichment
  23. 2026-09-16 17:11 UTCGHSA enrichment
  24. 2026-09-16 15:55 UTCEG score recompute
  25. 2026-09-16 15:55 UTCGHSA enrichment
  26. 2026-09-16 14:07 UTCEPSS rescore
  27. 2026-09-16 05:29 UTCEG score recompute
  28. 2026-09-16 05:29 UTCGHSA enrichment
  29. 2026-09-16 05:14 UTCEPSS rescore
  30. 2026-09-15 03:04 UTCGHSA enrichment
  31. 2026-09-13 22:30 UTCEG score recompute
  32. 2026-09-13 22:30 UTCGHSA enrichment
  33. 2026-09-13 16:46 UTCEPSS rescore
  34. 2026-09-13 00:19 UTCEG score recompute
  35. 2026-09-13 00:19 UTCGHSA enrichment
  36. 2026-09-12 15:00 UTCEPSS rescore
  37. 2026-09-12 02:07 UTCEG score recompute
  38. 2026-09-12 02:07 UTCGHSA enrichment
  39. 2026-09-11 14:52 UTCEPSS rescore
  40. 2026-09-11 09:36 UTCEPSS rescore
  41. 2026-09-11 03:56 UTCEG score recompute
  42. 2026-09-11 03:56 UTCGHSA enrichment
  43. 2026-09-10 09:34 UTCEPSS rescore
  44. 2026-09-10 05:43 UTCGHSA enrichment
  45. 2026-09-09 07:06 UTCEG score recompute
  46. 2026-09-09 07:06 UTCGHSA enrichment
  47. 2026-09-08 22:00 UTCEPSS rescore
  48. 2026-09-07 19:36 UTCEG score recompute
  49. 2026-09-07 19:36 UTCGHSA enrichment
  50. 2026-09-07 16:01 UTCEPSS rescore
  51. 2026-09-06 13:47 UTCEPSS rescore
  52. 2026-09-06 07:45 UTCEG score recompute
  53. 2026-09-06 07:45 UTCGHSA enrichment
  54. 2026-09-05 09:32 UTCEG score recompute
  55. 2026-09-05 09:32 UTCGHSA enrichment
  56. 2026-09-04 11:21 UTCEG score recompute
  57. 2026-09-04 11:21 UTCGHSA enrichment
  58. 2026-09-04 05:06 UTCEPSS rescore
  59. 2026-09-03 09:13 UTCEG score recompute
  60. 2026-09-03 09:13 UTCGHSA enrichment
  61. 2026-09-02 14:11 UTCEPSS rescore
  62. 2026-09-01 22:34 UTCEG score recompute
  63. 2026-09-01 22:34 UTCGHSA enrichment
  64. 2026-09-01 13:53 UTCEPSS rescore
  65. 2026-08-31 23:26 UTCGHSA enrichment
  66. 2026-08-30 20:33 UTCEG score recompute
  67. 2026-08-30 20:33 UTCGHSA enrichment
  68. 2026-08-30 19:17 UTCEPSS rescore
  69. 2026-08-30 01:22 UTCEPSS rescore
  70. 2026-08-29 22:23 UTCEG score recompute
  71. 2026-08-29 22:23 UTCGHSA enrichment
  72. 2026-08-28 21:41 UTCEPSS rescore
  73. 2026-08-28 00:57 UTCEG score recompute
  74. 2026-08-28 00:57 UTCGHSA enrichment
  75. 2026-08-27 14:25 UTCEPSS rescore

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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 on July 31, 2026, with the most recent update on September 16, 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 0.4% probability of exploitation in the next 30 days (32nd percentile of EPSS-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?
A fix for CVE-2026-18209 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-18209 are linked in the Vendor Advisories panel on this page.

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