What is the CVSS score of CVE-2026-15554?

CVE-2026-15554 has a CVSS 3.1 base score of 7.4 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.2%.

Which versions of Undertow are affected by CVE-2026-15554?

Undertow's AJP listener unconditionally trusts client certificate attributes without validation, allowing authenticated users on internal networks to impersonate any X.509 identity and bypass…. A patch is available.

How to fix or mitigate CVE-2026-15554?

Within 24 hours, locate all Undertow deployments and immediately restrict firewall access to port 8009 to only trusted reverse-proxy IPs; disable AJP entirely if not required for your proxy integration. Within 7 days, audit your reverse-proxy-to-Undertow network path to confirm AJP port is not exposed to broader internal subnets, and verify CLIENT-CERT validation is enforced at both proxy and Undertow layers. Within 30 days, migrate to reverse proxy solutions that do not require exposed AJP ports (e.g., HTTP/HTTPS-only proxying), implement mutual TLS between proxy and Undertow backend to authenticate the connection itself, or upgrade to a patched Undertow version once available from the vendor.

Undertow CVE-2026-15554

EUVD-2026-55981 HIGH

Improper Certificate Validation (CWE-295)

2026-08-11 secalert@redhat.com

GHSA-f478-cwfc-jqh3

Authentication Bypass

7.4

CVSS 3.1 · Vendor: redhat

Severity by source

Vendor (redhat) PRIMARY

7.4 HIGH

AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

vuln.today AI

7.4 HIGH

AV:N because AJP is a TCP network protocol; AC:H because direct port 8009 access is typically firewalled; PR:N and UI:N confirmed by description; no availability impact identified.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Red Hat

7.4 HIGH

qualitative

Primary rating from Vendor (redhat).

CVSS VectorVendor: redhat

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Aug 11, 2026 - 09:32 vuln.today

CVE Published

Aug 11, 2026 - 09:17 nvd

HIGH 7.4

DescriptionCVE.org

the Undertow AJP listener honours forged ssl_cert and is_ssl AJP attributes without requiring any shared-secret authentication. This enables an unauthenticated attacker with direct TCP access to port 8009 to bypass CLIENT-CERT authentication by injecting a forged X.509 certificate via the AJP protocol.

AnalysisAI

Undertow's AJP listener unconditionally trusts the ssl_cert and is_ssl AJP request attributes without requiring a shared-secret, allowing an unauthenticated remote attacker with direct TCP access to port 8009 to impersonate any X.509 client certificate identity and bypass CLIENT-CERT mutual TLS authentication entirely. Deployments where Undertow acts as a back-end behind a reverse proxy - with CLIENT-CERT authentication enforced at the proxy layer but the AJP port exposed on an internal network - are directly at risk of identity spoofing and authorization bypass. No public exploit code has been identified at time of analysis, and this CVE does not appear in the CISA KEV catalog; however, the bypass primitive is architecturally simple for any attacker who has obtained internal network access to the AJP port.

Technical ContextAI

Undertow is a high-performance Java web server used as the embedded HTTP engine in Red Hat JBoss EAP and WildFly, as well as directly in Quarkus applications. The AJP (Apache JServ Protocol, typically port 8009) connector allows a front-end web server such as Apache httpd (mod_proxy_ajp) to forward requests to the back-end Undertow instance, passing TLS metadata - including whether the connection was SSL (is_ssl) and the client's X.509 certificate (ssl_cert) - as AJP packet attributes. CWE-295 (Improper Certificate Validation) is the root cause class: Undertow performs no integrity validation of these forwarded attributes, specifically it does not enforce the AJP secret directive that was introduced as a mitigation for the related Ghostcat class of vulnerabilities (CVE-2020-1745 family). Because ssl_cert is accepted at face value, an attacker speaking raw AJP to port 8009 can present an arbitrary certificate value and be treated by the application as a fully authenticated CLIENT-CERT principal. The flaw exists entirely within the AJP attribute-handling logic, not in TLS itself.

RemediationAI

The primary remediation is to apply the vendor-issued patch from Red Hat once available - the fix version was not independently confirmed in the available source data, so monitor https://access.redhat.com/security/cve/CVE-2026-15554 and https://bugzilla.redhat.com/show_bug.cgi?id=2480601 for the patched release. Until a patch is applied, the most effective compensating control is to configure an AJP shared secret in Undertow's AJP connector (the 'secret' attribute in the server configuration) and require the corresponding secret on the Apache httpd mod_proxy_ajp side - this prevents unauthenticated parties from speaking AJP to port 8009 and is the architecturally correct mitigation for this class of flaw. As a secondary control, restrict port 8009 at the network or host firewall to only allow connections from the designated front-end proxy IP address, eliminating direct attacker access; this reduces risk without requiring application changes but does not address the root trust issue if the proxy host itself is compromised. If CLIENT-CERT authentication is not actively used in the deployment, consider disabling that authentication mode to reduce the blast radius of the flaw, though this may affect legitimate application functionality.