CVE-2026-18209

MEDIUMNVD 4.74.7
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This medium-severity CVE scores 4.7 under NVD CVSS v3. EPSS exploit probability: 0.4% (35th percentile of EPSS-scored CVEs). GitHub Security Advisory CVSS 3.4 is lower than this score; a lower GitHub score revises it only when its advisory is newer than the CVE record's last change, and this advisory (published 2026-07-31) is not newer than that change (2026-09-16), so it does not.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3

Also known asEUVD-2026-51487 (ENISA EUVD) · GHSA-c8xx-fr3x-6m5w (GitHub Security Advisories)Source: ENISA EUVD

4.7EG
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: 0.4%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 21/100

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)
Severity47% × 45%
Impact severity (EG Severity): CVSS 4.7 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.4% × 40%
FIRST EPSS: the 30-day exploitation probability 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
0.4%
EPSS %ILE
35th
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 (4.7): severity, escalated by confirmed exploitation. This CVE's 4.7 is its impact severity (EG Severity), not escalated.

EG Severity
4.7 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-24). 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

July 31, 2026

Last Modified

September 16, 2026

Advisory Details (2)

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

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
Red HatMentions a patch (unverified)

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 7× in last 7d / 48× 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.

Showing the most recent 100 of 215 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 115 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  2. 2026-10-31 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  3. 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  4. 2026-10-29 16:32 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  5. 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.4% · 35th percentile
  6. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.4% · 34th percentile
  7. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.4% · 34th percentile
  8. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
  9. 2026-10-25 14:45 UTCEG score recompute
  10. 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.4% · 34th percentile
  11. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.4% · 34th percentile
  12. 2026-10-23 06:00 UTCEG score recompute
  13. 2026-10-23 06:00 UTCVendor advisory
  14. 2026-10-23 06:00 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  15. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  16. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  17. 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  18. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  19. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  20. 2026-10-18 03:59 UTCEG score recompute
  21. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  22. 2026-10-16 16:40 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  23. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  24. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  25. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
Show 75 more
  1. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  2. 2026-10-12 16:27 UTCEG score recompute
  3. 2026-10-11 20:07 UTCEG score recompute
  4. 2026-10-11 17:20 UTCEG score recompute
  5. 2026-10-11 14:52 UTCEG score recompute
  6. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  7. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  8. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  9. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.4% · 33rd percentile
  10. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  11. 2026-10-06 23:51 UTCEG score recompute
  12. 2026-10-06 23:51 UTCVendor advisory
  13. 2026-10-06 23:51 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  14. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  15. 2026-10-05 19:57 UTCEG score recompute
  16. 2026-10-05 19:57 UTCVendor advisory
  17. 2026-10-05 19:56 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  18. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  19. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  20. 2026-10-04 06:33 UTCEG score recompute
  21. 2026-10-04 06:33 UTCVendor advisory
  22. 2026-10-04 06:33 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  23. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  24. 2026-10-02 16:51 UTCEG score recompute
  25. 2026-10-02 16:51 UTCVendor advisory
  26. 2026-10-02 16:51 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  27. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  28. 2026-10-01 02:48 UTCEG score recompute
  29. 2026-10-01 02:48 UTCVendor advisory
  30. 2026-10-01 02:48 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  31. 2026-09-30 15:02 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  32. 2026-09-29 15:20 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  33. 2026-09-29 06:50 UTCEG score recompute
  34. 2026-09-29 06:50 UTCVendor advisory
  35. 2026-09-29 06:50 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  36. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  37. 2026-09-27 18:57 UTCEG score recompute
  38. 2026-09-27 18:57 UTCVendor advisory
  39. 2026-09-27 18:57 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  40. 2026-09-27 13:47 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  41. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  42. 2026-09-25 07:56 UTCEG score recompute
  43. 2026-09-25 07:56 UTCVendor advisory
  44. 2026-09-25 07:56 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  45. 2026-09-24 09:45 UTCEG score recompute
  46. 2026-09-24 09:45 UTCVendor advisory
  47. 2026-09-24 09:45 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  48. 2026-09-23 11:35 UTCEG score recompute
  49. 2026-09-23 11:35 UTCVendor advisory
  50. 2026-09-23 11:35 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  51. 2026-09-22 13:23 UTCEG score recompute
  52. 2026-09-22 13:23 UTCVendor advisory
  53. 2026-09-22 13:23 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  54. 2026-09-19 23:43 UTCEG score recompute
  55. 2026-09-19 23:43 UTCVendor advisory
  56. 2026-09-19 23:43 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  57. 2026-09-18 23:28 UTCEG score recompute
  58. 2026-09-18 23:28 UTCVendor advisory
  59. 2026-09-18 23:28 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  60. 2026-09-18 19:27 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  61. 2026-09-18 01:17 UTCEG score recompute
  62. 2026-09-18 01:17 UTCVendor advisory
  63. 2026-09-18 01:17 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  64. 2026-09-16 19:20 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  65. 2026-09-16 18:53 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  66. 2026-09-16 17:11 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  67. 2026-09-16 15:55 UTCEG score recompute
  68. 2026-09-16 15:55 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  69. 2026-09-16 14:07 UTCEPSS rescoreEPSS 0.2% · 9th percentile
  70. 2026-09-16 05:29 UTCEG score recompute
  71. 2026-09-16 05:29 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  72. 2026-09-16 05:14 UTCEPSS rescoreEPSS 0.2% · 9th percentile
  73. 2026-09-15 03:04 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4
  74. 2026-09-13 22:30 UTCEG score recompute
  75. 2026-09-13 22:30 UTCGHSA enrichmentGHSA-c8xx-fr3x-6m5w · GitHub severity LOW · GitHub CVSS 3.4

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Frequently asked(5)

What is CVE-2026-18209?
CVE-2026-18209 is a medium-severity vulnerability; its CVE record was 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 made public?
CVE-2026-18209 was made public on July 28, 2026: that is the date its CVE record's CNA, Red Hat, Inc., gives for when the vulnerability was made public. The CVE record itself was published on July 31, 2026. EchelonGraph's copy of the record carries a last-modified date of September 16, 2026; the record at its source may have been updated since.
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 (35th 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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