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Full vulnerability report · 2026
CVE-2026-18209High confidence

Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check

Red Hat · Red Hat build of Keycloak 26.6

Official source article: Red Hat RHSA-2026:68277 ↗. Check the applicable product and release in the original source.

3.4LowCVSS 3.1
Recommended action
Scheduled

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityLowOperational priority:Low, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • EPSS is 0.41% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Red Hat Red Hat build of Keycloak 26.6 and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: No default targetRemediation target: Normal maintenance

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-18209 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykeycloak-services: keycloak-services: OIDC redirect_uri fragment bypass in HTTP parameter pollution check
10 fixed

The vendor explicitly identifies these products or versions as containing the fix.

  • rhbk/keycloak-operator-bundle@sha256:214bd43b28c8f61d9c8f81f57e9dd3027d09cb3c00fb307bd265130147dd419b_amd64 as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9-operator@sha256:17799b1e42dac3e81023c17319e0250b89d0fd689e2910b57443e311f2810ef2_arm64 as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9-operator@sha256:9f74c98693761db4e065a3d7a28b04c8f60abcb37b6cc48bd4926cbbb5e3e788_ppc64le as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9-operator@sha256:de43455a4604ac89363ee40c3fe8f8641b905380413a1abd91ee7d3416e6a356_amd64 as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9-operator@sha256:eeb387096bac9dd17f2a7e48071602ef4e27902204cbe8856c3f04303212d6a6_s390x as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9@sha256:118e76caf2bb91d04091c2e7dc20a163fcb9b218e44fd5f2ca298db669eed059_ppc64le as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9@sha256:2b0f46c7a7aa9c580d509030054bb5f4a233f9ec38e2c79e7b0c98b9b0f79d96_s390x as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9@sha256:3eac2479ff615aa8ab099e7b669a98dd6978753b7dc51582fe899ac756ae18f4_arm64 as a component of Red Hat build of Keycloak 26.6
  • rhbk/keycloak-rhel9@sha256:7711b8114aef173846b601a776d85640832b371421c57b6506e5df334ed96dd6_amd64 as a component of Red Hat build of Keycloak 26.6
  • Red Hat build of Keycloak 26.6.7
Summary
A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.
Remediation
Before applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-51487

No EUVD known-exploited evidence

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
3.4 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Low technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

What

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

Why

The product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

Why

The product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.

How

An attacker operating through a network path may attempt exploitation without authentication after a user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Validation of Consistency within Input → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
Required interaction required
Attack complexity
High: exploitation depends on specific conditions
Security boundary
Changed: exploitation can affect a different security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-1288 ↗

CWE-1288: Improper Validation of Consistency within Input. The product receives a complex input with multiple elements or fields that must be consistent with each other, but it does not validate or incorrectly validates that the input is actually consistent.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACHighAttack complexity: Successful exploitation depends on specific conditions outside the attacker's direct control.PRNonePrivileges required: The attacker does not need an account or existing privileges.UIRequiredUser interaction: Another user must perform an action for exploitation to succeed.SChangedScope: The attack can affect a component governed by a different security authority.CNoneConfidentiality impact: No direct loss is represented by this metric.ILowIntegrity impact: A successful attack can cause a limited loss.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-1288
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-51487Official EUVD mapping

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

Official EUVD record ↗
BSI · German · WID-SEC-2026-2614Keycloak: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Keycloak ausnutzen, um seine Privilegien zu erhöhen, Sicherheitsmaßnahmen zu umgehen, Daten zu manipulieren und sensible Informationen offenzulegen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260805Security Bulletin 5 Aug 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 5 Aug 2026, published on 5 August 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-027474レッドハットのbuild of keycloakにおける入力の一貫性の検証に関する脆弱性

Keycloakのkeycloak-servicesコンポーネントに脆弱性が発見されました。このコンポーネントはOpenID Connect（OIDC）認証フローを処理しています。この問題は、HTTPパラメータ汚染を防ぐためのセキュリティチェックがリダイレクトURLのクエリ部分のみを検査し、フラグメント部分を無視しているために発生します。クライアントがワイルドカードのリダイレクトURIで構成されている場合、攻撃者はこれを利用してログイン応答に重複したセキュリティパラメータを注入できます。クライアントアプリケーションが正しく構成されていないと、Keycloakからの正規のセキュリティ情報ではなく、攻撃者が注入したデータを信頼してしまい、セッション固定やアカウントの混同を引き起こす可能性があることが判明しています。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Red Hat build of Keycloak 26.6: patch: 26.6.7-3, patch: 26.6-20
Fixed
Action
Before applying the update, back up your existing installation, including all applications, configuration files, databases and database settings, and so on.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 31 Jul 2026 · Last source change 16 Sept 2026, 18:36 UTC · CWE-1288 · Improper Validation of Consistency within Input

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-51487
Product sourceCNA
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment

Missing structured fields: affected versions. Missing data is not evidence of low risk; review the primary advisory.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    See the vendor and CVE records for the affected range. · Fixed: Red Hat build of Keycloak 26.6: 26.6-20 < *, 26.6.7-3 < *
    After
    See the vendor and CVE records for the affected range. · Fixed: Red Hat build of Keycloak 26.6: 26.6.7-3 < *, 26.6-20 < *
    CNA ↗
  2. Affected versionsThe structured affected or fixed version information changed.
    Before
    Fixed: Red Hat build of Keycloak 26.6.7
    After
    Fixed: rhbk/keycloak-operator-bundle@sha256:214bd43b28c8f61d9c8f81f57e9dd3027d09cb3c00fb307bd265130147dd419b_amd64 as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9-operator@sha256:17799b1e42dac3e81023c17319e0250b89d0fd689e2910b57443e311f2810ef2_arm64 as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9-operator@sha256:9f74c98693761db4e065a3d7a28b04c8f60abcb37b6cc48bd4926cbbb5e3e788_ppc64le as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9-operator@sha256:de43455a4604ac89363ee40c3fe8f8641b905380413a1abd91ee7d3416e6a356_amd64 as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9-operator@sha256:eeb387096bac9dd17f2a7e48071602ef4e27902204cbe8856c3f04303212d6a6_s390x as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9@sha256:118e76caf2bb91d04091c2e7dc20a163fcb9b218e44fd5f2ca298db669eed059_ppc64le as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9@sha256:2b0f46c7a7aa9c580d509030054bb5f4a233f9ec38e2c79e7b0c98b9b0f79d96_s390x as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9@sha256:3eac2479ff615aa8ab099e7b669a98dd6978753b7dc51582fe899ac756ae18f4_arm64 as a component of Red Hat build of Keycloak 26.6; rhbk/keycloak-rhel9@sha256:7711b8114aef173846b601a776d85640832b371421c57b6506e5df334ed96dd6_amd64 as a component of Red Hat build of Keycloak 26.6; Red Hat build of Keycloak 26.6.7
    Red Hat Product Security ↗
  3. Vendor guidanceAuthoritative vendor guidance changed: removed vendor advisory: access.redhat.com/RHSA-2026:68277; removed vendor advisory: access.redhat.com/RHSA-2026:68278.
    Before
    remediation: access.redhat.com/RHSA-2026:68277 · vendor advisory: access.redhat.com/CVE-2026-18209 · vendor advisory: access.redhat.com/RHSA-2026:68277 · 2 more references
    After
    remediation: access.redhat.com/RHSA-2026:68277 · vendor advisory: access.redhat.com/CVE-2026-18209 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2508305
    secalert@redhat.com ↗
  4. Vendor guidanceAuthoritative vendor guidance changed: added remediation: access.redhat.com/RHSA-2026:68277; added vendor advisory: access.redhat.com/RHSA-2026:68277; 1 further additions.
    Before
    vendor advisory: access.redhat.com/CVE-2026-18209 · vendor advisory: bugzilla.redhat.com/show_bug.cgi?id=2508305
    After
    remediation: access.redhat.com/RHSA-2026:68277 · vendor advisory: access.redhat.com/CVE-2026-18209 · vendor advisory: access.redhat.com/RHSA-2026:68277 · 2 more references
    access.redhat.com ↗
  5. Affected versionsThe structured affected or fixed version information changed.
    Before
    See the vendor and CVE records for the affected range. · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    See the vendor and CVE records for the affected range. · Fixed: Red Hat build of Keycloak 26.6: 26.6-20 < *, 26.6.7-3 < *
    CNA ↗
  6. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    access.redhat.com ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-51487↗Vendor advisory↗Vendor advisory↗CVE authority or vendor reference · Red Hat RHSA-2026:68277↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-18209 · cve.blacktree.nl