A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in a Denial of Service (DoS) for the Keycloak server.

The remote Redhat Enterprise Linux 7 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:76128 advisory.

    Red Hat Single Sign-On 7.6 is a standalone server, based on the Keycloak project, that provides     authentication and standards-based single sign-on capabilities for web and mobile applications.

    This release of Red Hat Single Sign-On 7.6.13 on RHEL 7 serves as a replacement for Red Hat Single Sign-On     7.6.12, and includes bug fixes and enhancements, which are documented in the Release Notes document linked     to in the References.

    Security Fix(es):
    * undertow-core: Undertow MadeYouReset HTTP/2 DDoS Vulnerability (CVE-2025-9784)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Information disclosure and data deletion via second-order SQL injection (CVE-2026-0603)
    * GOSTCTR implementation unable to process more than 255 blocks correctly (CVE-2025-14813)
    * PKIX draft CompositeVerifier accepts empty signature sequence as valid (CVE-2026-5588)
    * unbounded PGP AEAD chunk size leads to pre-auth resource exhaustion (CVE-2026-3505)
    * High integrity impact due to improper DNS domain name constraint enforcement (CVE-2026-42579)
    * HTTP Request Smuggling due to improper handling of conflicting HTTP/1.0 headers (CVE-2026-42581)
    * HTTP Header Injection via HttpProxyHandler Disabled Validation (CVE-2026-42578)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * IPv6 subnet rule bypass due to incorrect masking operation (CVE-2026-44249)
    * Denial of Service via malformed HAProxy message (CVE-2026-44893)
    * Denial of Service due to resource leak (CVE-2026-48043)
    * Netty HAProxy PROXY protocol v2 codec: Denial of Service via memory leak from crafted PROXY protocol     headers (CVE-2026-48059)
    * Netty has Insufficient Bailiwick Validation for NS Records (CVE-2026-47691)
    * Improper trust manager handling leads to hostname verification bypass (CVE-2026-50010)
    * Information disclosure and data manipulation due to improper CNAME record validation (CVE-2026-45674)
    * Denial of Service due to eager buffer allocation in TLS handshake (CVE-2026-45416)
    * Arbitrary code execution via PolymorphicTypeValidator bypass (CVE-2026-54512)
    * Denial of Service via deeply nested JSON processing (CVE-2026-50193)
    * Denial of Service via incomplete fix in async JSON parser (CVE-2026-68494)
    * Missing authentication on EAP's IIOP NameService leads to MITM or DoS (CVE-2026-15563)
    * Session fixation in OIDC login flow that can lead to account takeover (CVE-2026-7507)
    * Denial of Service via specially crafted SAML input (CVE-2026-7307)
    * Denial of Service due to excessive SAMLRequest decompression (CVE-2026-2575)
    * Denial of Service via excessive processing of OpenID Connect scope parameters (CVE-2026-4634)
    * Unauthorized access via improper validation of encrypted SAML assertions (CVE-2026-2092)

    For more details about the security issue(s), including the impact, a CVSS score, and other related     information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Redhat Enterprise Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:76129 advisory.

    Red Hat Single Sign-On 7.6 is a standalone server, based on the Keycloak project, that provides     authentication and standards-based single sign-on capabilities for web and mobile applications.

    This release of Red Hat Single Sign-On 7.6.13 on RHEL 8 serves as a replacement for Red Hat Single Sign-On     7.6.12, and includes bug fixes and enhancements, which are documented in the Release Notes document linked     to in the References.

    Security Fix(es):
    * undertow-core: Undertow MadeYouReset HTTP/2 DDoS Vulnerability (CVE-2025-9784)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Information disclosure and data deletion via second-order SQL injection (CVE-2026-0603)
    * GOSTCTR implementation unable to process more than 255 blocks correctly (CVE-2025-14813)
    * PKIX draft CompositeVerifier accepts empty signature sequence as valid (CVE-2026-5588)
    * unbounded PGP AEAD chunk size leads to pre-auth resource exhaustion (CVE-2026-3505)
    * High integrity impact due to improper DNS domain name constraint enforcement (CVE-2026-42579)
    * HTTP Request Smuggling due to improper handling of conflicting HTTP/1.0 headers (CVE-2026-42581)
    * HTTP Header Injection via HttpProxyHandler Disabled Validation (CVE-2026-42578)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * IPv6 subnet rule bypass due to incorrect masking operation (CVE-2026-44249)
    * Denial of Service via malformed HAProxy message (CVE-2026-44893)
    * Denial of Service due to resource leak (CVE-2026-48043)
    * Netty HAProxy PROXY protocol v2 codec: Denial of Service via memory leak from crafted PROXY protocol     headers (CVE-2026-48059)
    * Netty has Insufficient Bailiwick Validation for NS Records (CVE-2026-47691)
    * Improper trust manager handling leads to hostname verification bypass (CVE-2026-50010)
    * Information disclosure and data manipulation due to improper CNAME record validation (CVE-2026-45674)
    * Denial of Service due to eager buffer allocation in TLS handshake (CVE-2026-45416)
    * Arbitrary code execution via PolymorphicTypeValidator bypass (CVE-2026-54512)
    * Denial of Service via deeply nested JSON processing (CVE-2026-50193)
    * Denial of Service via incomplete fix in async JSON parser (CVE-2026-68494)
    * Missing authentication on EAP's IIOP NameService leads to MITM or DoS (CVE-2026-15563)
    * Session fixation in OIDC login flow that can lead to account takeover (CVE-2026-7507)
    * Denial of Service via specially crafted SAML input (CVE-2026-7307)
    * Denial of Service due to excessive SAMLRequest decompression (CVE-2026-2575)
    * Denial of Service via excessive processing of OpenID Connect scope parameters (CVE-2026-4634)
    * Unauthorized access via improper validation of encrypted SAML assertions (CVE-2026-2092)

    For more details about the security issue(s), including the impact, a CVSS score, and other related     information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Redhat Enterprise Linux 9 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:76130 advisory.

    Red Hat Single Sign-On 7.6 is a standalone server, based on the Keycloak project, that provides     authentication and standards-based single sign-on capabilities for web and mobile applications.

    This release of Red Hat Single Sign-On 7.6.13 on RHEL 9 serves as a replacement for Red Hat Single Sign-On     7.6.12, and includes bug fixes and enhancements, which are documented in the Release Notes document linked     to in the References.

    Security Fix(es):
    * undertow-core: Undertow MadeYouReset HTTP/2 DDoS Vulnerability (CVE-2025-9784)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Undertow HTTP Server Fails to Reject Malformed Host Headers Leading to Potential Cache Poisoning and     SSRF (CVE-2025-12543)
    * Information disclosure and data deletion via second-order SQL injection (CVE-2026-0603)
    * GOSTCTR implementation unable to process more than 255 blocks correctly (CVE-2025-14813)
    * PKIX draft CompositeVerifier accepts empty signature sequence as valid (CVE-2026-5588)
    * unbounded PGP AEAD chunk size leads to pre-auth resource exhaustion (CVE-2026-3505)
    * High integrity impact due to improper DNS domain name constraint enforcement (CVE-2026-42579)
    * HTTP Request Smuggling due to improper handling of conflicting HTTP/1.0 headers (CVE-2026-42581)
    * HTTP Header Injection via HttpProxyHandler Disabled Validation (CVE-2026-42578)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * Denial of Service via unbounded memory allocation in HTTP content decompression (CVE-2026-42587)
    * IPv6 subnet rule bypass due to incorrect masking operation (CVE-2026-44249)
    * Denial of Service via malformed HAProxy message (CVE-2026-44893)
    * Denial of Service due to resource leak (CVE-2026-48043)
    * Netty HAProxy PROXY protocol v2 codec: Denial of Service via memory leak from crafted PROXY protocol     headers (CVE-2026-48059)
    * Netty has Insufficient Bailiwick Validation for NS Records (CVE-2026-47691)
    * Improper trust manager handling leads to hostname verification bypass (CVE-2026-50010)
    * Information disclosure and data manipulation due to improper CNAME record validation (CVE-2026-45674)
    * Denial of Service due to eager buffer allocation in TLS handshake (CVE-2026-45416)
    * Arbitrary code execution via PolymorphicTypeValidator bypass (CVE-2026-54512)
    * Denial of Service via deeply nested JSON processing (CVE-2026-50193)
    * Denial of Service via incomplete fix in async JSON parser (CVE-2026-68494)
    * Missing authentication on EAP's IIOP NameService leads to MITM or DoS (CVE-2026-15563)
    * Session fixation in OIDC login flow that can lead to account takeover (CVE-2026-7507)
    * Denial of Service via specially crafted SAML input (CVE-2026-7307)
    * Denial of Service due to excessive SAMLRequest decompression (CVE-2026-2575)
    * Denial of Service via excessive processing of OpenID Connect scope parameters (CVE-2026-4634)
    * Unauthorized access via improper validation of encrypted SAML assertions (CVE-2026-2092)

    For more details about the security issue(s), including the impact, a CVSS score, and other related     information, refer to the CVE page(s) listed in the References section.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - A flaw was found in Keycloak. An unauthenticated attacker can exploit this vulnerability by sending a
    specially crafted POST request with an excessively long scope parameter to the OpenID Connect (OIDC) token
    endpoint. This leads to high resource consumption and prolonged processing times, ultimately resulting in
    a Denial of Service (DoS) for the Keycloak server. (CVE-2026-4634)

Keycloak installed on the remote host is 26.2.x prior to 26.2.15, 26.4.x prior to  26.4.11, 26.5.x prior to 26.5.7 are affected by multiple vulnerabilities:

  - A privilege escalation flaw exists due to improper isolation in the SingleUseObjectProvider. An     unauthenticated, remote attacker can forge authorization codes and potentially obtain admin-capable     access tokens. (CVE-2026-4282)

  - A denial of service flaw exists in the OpenID Connect token endpoint. An unauthenticated, remote     attacker can exhaust server CPU and memory by sending an excessively long scope parameter.
    (CVE-2026-4634)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Type	Severity
363386	RHEL 7 : Red Hat Single Sign-On 7.6.13 security update on RHEL 7 (Important) (RHSA-2026:76128)	Nessus	Red Hat Local Security Checks	Local	critical
363126	RHEL 8 : Red Hat Single Sign-On 7.6.13 security update on RHEL 8 (Important) (RHSA-2026:76129)	Nessus	Red Hat Local Security Checks	Local	critical
363125	RHEL 9 : Red Hat Single Sign-On 7.6.13 security update on RHEL 9 (Important) (RHSA-2026:76130)	Nessus	Red Hat Local Security Checks	Local	critical
461658	Echo: org.keycloak:keycloak-services: security update to 26.5.7	Tenable Cloud Security	Echo Local Security Checks	Local	high
461658	Echo: org.keycloak:keycloak-services: security update to 26.5.7	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	high
330085	Keycloak 26.2 < 26.2.15 / 26.4 < 26.4.11 / 26.5 < 26.5.7 Multiple Vulnerabilities	Nessus	Misc.	Local	high
439847	SCA: security update for org.keycloak:keycloak-services (GHSA-h4wv-g838-66g3)	Tenable Cloud Security	SCA Checks	Local	high
439847	SCA: security update for org.keycloak:keycloak-services (GHSA-h4wv-g838-66g3)	Tenable Self-Hosted Container Security	SCA Checks	Local	high

Detections

Analytics

CVE-2026-4634

high

Tenable Plugins

critical

critical

critical

high

high

high

high

high