CVE-2026-37977

MEDIUMNVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under NVD CVSS v3. EPSS exploit probability: 0.3%, top 83% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 5.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the azp claim from a client-supplied JSON Web Token (JWT) is used to set the Access-Control-Allow-Origin header before the JWT signature is validated. When a specially crafted JWT with an attacker-controlled azp value is processed, this value is reflected as the CORS origin, even if the grant is later rejected. This can lead to the exposure of low-sensitivity information from authorization server error responses, weakening origin isolation, but only when a target client is misconfigured with webOrigins: ["*"].

CVSS v3
5.3
EG Score
5.3MEDIUMmedium confidence
EG Risk
24
EG Risk 24/100

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
Severity53% × 45%
Exploitation0% × 40%
Automatability0% × 15%
EPSS PROB
0.3%
EPSS %ILE
18th
KEV
Not listed

Published

April 6, 2026

Last Modified

June 26, 2026

Advisory Details (4)

Auto-updated Jun 26, 2026
Patch available. Sources: redhat.
redhat

2455324 – (CVE-2026-37977) CVE-2026-37977 keycloak: org.keycloak.protocol.oidc.grants.ciba: Keycloak: Information disclosure via CORS header injection due to unvalidated JWT azp claim

https://bugzilla.redhat.com/show_bug.cgi?id=2455324
redhatMentions a patch (unverified)

cve-details

https://access.redhat.com/security/cve/CVE-2026-37977
redhatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:25098
redhatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:25097

Vendor Advisories for CVE-2026-37977(5)

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

Patch Availability(4)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatrhbk/keycloak-rhel9-operator:26.4-192026-06-25redhat
redhatrhbk/keycloak-rhel92026-06-25redhat
redhatrhbk/keycloak-rhel9-operator:26.6-62026-06-10redhat
mavenorg.keycloak:keycloak-services—ghsa

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.

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
org.keycloak:keycloak-services26.5.0 ... 26.6.2 (11 versions)
  • every version up to 26.4.13: fixed in 26.4.13
  • 26.5.0 up to 26.6.3: fixed in 26.6.3
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 7× in last 7d / 25× 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 183 total refreshes for this CVE.

  1. 2026-10-09 20:07 UTCEPSS rescore
  2. 2026-10-08 17:12 UTCEPSS rescore
  3. 2026-10-07 23:48 UTCEPSS rescore
  4. 2026-10-06 15:17 UTCEPSS rescore
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  8. 2026-10-01 19:49 UTCEPSS rescore
  9. 2026-09-30 15:03 UTCEPSS rescore
  10. 2026-09-28 13:51 UTCEPSS rescore
  11. 2026-09-27 13:48 UTCEPSS rescore
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  21. 2026-09-13 16:47 UTCEPSS rescore
  22. 2026-09-12 15:01 UTCEPSS rescore
  23. 2026-09-11 14:53 UTCEPSS rescore
  24. 2026-09-11 09:37 UTCEPSS rescore
  25. 2026-09-10 09:34 UTCEPSS rescore
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  1. 2026-09-08 22:00 UTCEPSS rescore
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  3. 2026-09-06 13:47 UTCEPSS rescore
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  5. 2026-09-02 14:12 UTCEPSS rescore
  6. 2026-09-01 13:53 UTCEPSS rescore
  7. 2026-09-01 04:39 UTCEPSS rescore
  8. 2026-08-30 19:17 UTCEPSS rescore
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  10. 2026-08-28 21:41 UTCEPSS rescore
  11. 2026-08-27 14:25 UTCEPSS rescore
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  13. 2026-08-25 13:49 UTCEPSS rescore
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  17. 2026-08-19 17:03 UTCEPSS rescore
  18. 2026-08-18 13:48 UTCEPSS rescore
  19. 2026-08-17 13:47 UTCEPSS rescore
  20. 2026-08-16 14:56 UTCEPSS rescore
  21. 2026-08-16 08:26 UTCEG score recompute
  22. 2026-08-16 08:26 UTCVendor advisory
  23. 2026-08-16 02:14 UTCEPSS rescore
  24. 2026-08-15 01:30 UTCEPSS rescore
  25. 2026-08-14 05:35 UTCEG score recompute
  26. 2026-08-14 05:35 UTCVendor advisory
  27. 2026-08-13 22:00 UTCEPSS rescore
  28. 2026-08-13 00:33 UTCEG score recompute
  29. 2026-08-13 00:33 UTCVendor advisory
  30. 2026-08-12 13:51 UTCEPSS rescore
  31. 2026-08-12 01:56 UTCEG score recompute
  32. 2026-08-12 01:56 UTCVendor advisory
  33. 2026-08-11 13:43 UTCEPSS rescore
  34. 2026-08-11 03:19 UTCEG score recompute
  35. 2026-08-11 03:19 UTCVendor advisory
  36. 2026-08-11 00:00 UTCEPSS rescore
  37. 2026-08-10 03:42 UTCEG score recompute
  38. 2026-08-10 03:42 UTCVendor advisory
  39. 2026-08-09 13:46 UTCEPSS rescore
  40. 2026-08-09 05:05 UTCEG score recompute
  41. 2026-08-09 05:05 UTCVendor advisory
  42. 2026-08-08 16:37 UTCEPSS rescore
  43. 2026-08-07 15:11 UTCEG score recompute
  44. 2026-08-07 15:11 UTCVendor advisory
  45. 2026-08-06 13:46 UTCEPSS rescore
  46. 2026-08-06 00:10 UTCEG score recompute
  47. 2026-08-06 00:10 UTCVendor advisory
  48. 2026-08-05 19:17 UTCEPSS rescore
  49. 2026-08-04 15:10 UTCEPSS rescore
  50. 2026-08-04 10:38 UTCEPSS rescore
  51. 2026-08-03 22:30 UTCEG score recompute
  52. 2026-08-03 22:30 UTCVendor advisory
  53. 2026-08-03 10:36 UTCEPSS rescore
  54. 2026-08-02 14:27 UTCEG score recompute
  55. 2026-08-02 14:27 UTCVendor advisory
  56. 2026-08-02 02:27 UTCEPSS rescore
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  69. 2026-07-23 03:10 UTCEG score recompute▲ 1.60
  70. 2026-07-22 14:08 UTCEPSS rescore
  71. 2026-07-21 15:24 UTCEPSS rescore
  72. 2026-07-20 17:08 UTCEPSS rescore
  73. 2026-07-19 14:31 UTCEPSS rescore
  74. 2026-07-19 02:29 UTCEPSS rescore
  75. 2026-07-18 10:04 UTCEPSS rescore

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Frequently asked(5)

What is CVE-2026-37977?
CVE-2026-37977 is a medium vulnerability published on April 6, 2026. A flaw was found in Keycloak. A remote attacker can exploit a Cross-Origin Resource Sharing (CORS) header injection vulnerability in Keycloak's User-Managed Access (UMA) token endpoint. This flaw occurs because the azp claim from a client-supplied JSON Web Token (JWT) is used to set the…
When was CVE-2026-37977 disclosed?
CVE-2026-37977 was first published on April 6, 2026, with the most recent update on June 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-37977 actively exploited?
CVE-2026-37977 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (18th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-37977?
CVE-2026-37977 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-37977?
A fix for CVE-2026-37977 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-37977 are linked in the Vendor Advisories panel on this page.

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