# CVE-2026-37977: Keycloak vulnerable to information disclosure via CORS header injection due to unvalidated JWT azp claim > Attackers can inject CORS headers via unvalidated JWT claims to expose low-sensitivity error data, requiring misconfigured webOrigins. - **Severity:** Low 3.7 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 6 Apr 2026 - **Updated:** 26 Jun 2026 - **Also known as:** ECHO-84f9-e9cf-32fc, GHSA-5v8v-xvjv-57x7, MINI-4jx5-hmg6-3qmv, MINI-7wm3-grjx-7m6q ## What is CVE-2026-37977? CVE-2026-37977 is a low-severity vulnerability in Redhat Build of Keycloak, published on 6 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description 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: ["*"]`. Weakness: CWE-346 (Origin Validation Error) ## Which versions are affected by CVE-2026-37977? 4 open source packages ship an affected version, including org.keycloak:keycloak-services. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `org.keycloak:keycloak-services` | Maven | All versions | 26.4.13 | | `org.keycloak:keycloak-services` | Maven | All versions | 26.4.13 | | `org.keycloak:keycloak-services` | Maven | From 26.5.0 | 26.6.3 | | `org.keycloak:keycloak-services` | Maven | From 26.5.0 | 26.6.3 | Products: Redhat Build of Keycloak. ## How do I fix CVE-2026-37977? Upgrade org.keycloak:keycloak-services to a fixed version for your release line: 26.4.13 or 26.6.3. ## Is CVE-2026-37977 being exploited? There is no known exploitation of CVE-2026-37977 in the wild and no public exploit code. ## Other vulnerabilities in Redhat Build of Keycloak - [CVE-2026-15572](https://insights.sbomify.com/CVE-2026-15572/): Keycloak-services: keycloak-services: dcr protocol mapper type-swap policy bypass allows privilege escalation (high 8.8) - [CVE-2026-3047](https://insights.sbomify.com/CVE-2026-3047/): Keycloak SAML Broken has Authentication Bypass by Primary Weakness (high 8.8) - [CVE-2026-15573](https://insights.sbomify.com/CVE-2026-15573/): Keycloak-services: keycloak-services: authorization bypass via unnormalized uri matching in pathmatcher (high 8.1) - [CVE-2026-16102](https://insights.sbomify.com/CVE-2026-16102/): Keycloak-services: keycloak-services: default dcr policy allows role forgery via user property mappers (high 8.1) - [CVE-2026-1609](https://insights.sbomify.com/CVE-2026-1609/): Org.keycloak/keycloak-quarkus-server: keycloak: unauthorized access via jwt authorization grant with disabled users (high 8.1) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-37977 and fix it if it is affected. What it is: CVE-2026-37977 is a low-severity vulnerability in Redhat Build of Keycloak, published on 6 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: There is no known exploitation of CVE-2026-37977 in the wild and no public exploit code. Affected packages and fixed versions: - org.keycloak:keycloak-services (Maven): affected all versions; fixed in 26.4.13 - org.keycloak:keycloak-services (Maven): affected all versions; fixed in 26.4.13 - org.keycloak:keycloak-services (Maven): affected from 26.5.0; fixed in 26.6.3 - org.keycloak:keycloak-services (Maven): affected from 26.5.0; fixed in 26.6.3 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-37977/ (Markdown: https://insights.sbomify.com/CVE-2026-37977/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-37977 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-37977 - OSV: https://osv.dev/vulnerability/CVE-2026-37977 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-37977/ Summaries are generated and may contain mistakes; the official description above is the record.