CVE-2026-37977 (GCVE-0-2026-37977)
Vulnerability from cvelistv5 – Published: 2026-04-06 08:38 – Updated: 2026-06-26 07:01
VLAI
EPSS
VEX
Title
Keycloak: org.keycloak.protocol.oidc.grants.ciba: keycloak: information disclosure via cors header injection due to unvalidated jwt azp claim
Summary
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: ["*"]`.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-06 11:55 UTC
CWE
- CWE-346 - Origin Validation Error
Assigner
References
6 references
| URL | Tags |
|---|---|
| https://access.redhat.com/errata/RHSA-2026:25097 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:25098 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:30049 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:30050 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/security/cve/CVE-2026-37977 | vdb-entryx_refsource_REDHAT |
| https://bugzilla.redhat.com/show_bug.cgi?id=2455324 | issue-trackingx_refsource_REDHAT |
Impacted products
6 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Red Hat | Red Hat build of Keycloak 26.4 |
Unaffected:
26.4.13-1 , < *
(rpm)
cpe:/a:redhat:build_keycloak:26.4::el9 |
||
| Red Hat | Red Hat build of Keycloak 26.4 |
Unaffected:
26.4-19 , < *
(rpm)
cpe:/a:redhat:build_keycloak:26.4::el9 |
||
| Red Hat | Red Hat build of Keycloak 26.4.13 |
cpe:/a:redhat:build_keycloak:26.4::el9
|
||
| Red Hat | Red Hat build of Keycloak 26.6 |
Unaffected:
26.6.3-3 , < *
(rpm)
cpe:/a:redhat:build_keycloak:26.6::el9 |
||
| Red Hat | Red Hat build of Keycloak 26.6 |
Unaffected:
26.6-6 , < *
(rpm)
cpe:/a:redhat:build_keycloak:26.6::el9 |
||
| Red Hat | Red Hat build of Keycloak 26.6.3 |
cpe:/a:redhat:build_keycloak:26.6::el9
|
Date Public
2026-04-06 08:34
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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