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Full vulnerability report · 2026
CVE-2026-18212High confidence

Keycloak-services: keycloak-services: saml redirect deflate helpers leak native zlib state

Red Hat · Red Hat build of Keycloak 26.4

Official source article: Red Hat RHSA-2026:68276 ↗. Check the applicable product and release in the original source.

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:High, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.52% 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 26.4 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: Within 30 daysRemediation target: Within 180 days

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-2026-18212 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykeycloak-services: keycloak-services: SAML Redirect DEFLATE helpers leak native zlib state
2 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • keycloak-services as a component of Red Hat Data Grid 8
  • keycloak-services as a component of Red Hat Single Sign-On 7
Summary
A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.
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-2026-80828

No EUVD known-exploited evidence

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

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
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

What

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

Why

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

Why

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

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 → Missing Release of Memory after Effective Lifetime → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-401 ↗

CWE-401: Missing Release of Memory after Effective Lifetime. The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

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:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
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.
NetworkUnauthenticatedDenial of serviceCWE-401
A

Official authority intelligence

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

ENISA EUVD · EUVD-2026-80828Official EUVD mapping

A flaw was found in the SAML Redirect Binding implementation of Keycloak, an open-source identity and access management solution. The issue occurs because the custom DEFLATE compression and decompression helpers fail to release native zlib memory after use. An unauthenticated attacker can exploit this by sending repeated malformed SAML requests, leading to native memory exhaustion and a denial of service.

Official EUVD record ↗
BSI · German · WID-SEC-2026-3418Keycloak: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Keycloak ausnutzen, um Sicherheitsvorkehrungen zu umgehen, um seine Privilegien zu erhöhen, um einen Denial of Service Angriff durchzuführen und um Informationen offenzulegen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260923Security Bulletin 23 Sep 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 23 Sep 2026, published on 23 September 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

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
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 16 Sept 2026 · Last source change 16 Sept 2026, 18:35 UTC · CWE-401 · Missing Release of Memory after Effective Lifetime

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 2026-09-17
European sourceENISA EUVD · EUVD-2026-80828
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD awaiting enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. ENISA EUVD mappingEUVD-2026-80828 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-80828"}
    ENISA EUVD ↗
  2. 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 26.4: 26.4-26 < *, 26.4.16-2 < *; 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 26.4: 26.4.16-2 < *, 26.4-26 < *; Red Hat build of Keycloak 26.6: 26.6.7-3 < *, 26.6-20 < *
    CNA ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    keycloak-services as a component of Red Hat Data Grid 8; keycloak-services as a component of Red Hat Single Sign-On 7 · Fixed: rhbk/keycloak-operator-bundle@sha256:f9f87b578925a866bb0a6eb85b96fc4d40d7a76508bcc042c47a870e038185d0_amd64 as a component of Red Hat build of Keycloak 26.4; Red Hat build of Keycloak 26.4.16; Red Hat build of Keycloak 26.6.7
    After
    keycloak-services as a component of Red Hat Data Grid 8; keycloak-services as a component of Red Hat Single Sign-On 7 · Fixed: rhbk/keycloak-operator-bundle@sha256:f9f87b578925a866bb0a6eb85b96fc4d40d7a76508bcc042c47a870e038185d0_amd64 as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9-operator@sha256:62295b1297796d71b1ae80dff660fa806915967fdbce2ed6b69bd6dd0d949970_arm64 as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9-operator@sha256:7f0849b3093db0b70f2448013d8960ffcc080465f09d7db3c0fe8f16c8ffe7a0_ppc64le as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9-operator@sha256:ba3dd6e11edd6da59f652f3c1ba1d015e93dfd61986c048750dd8b25556795b3_s390x as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9-operator@sha256:e108c6d85a4e70d52f7e6eda39e59cef9fbabea9412b08a9da0fec686da70615_amd64 as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9@sha256:0645b67de8c23ae9357ee892c6a9b61760f6d28f05d354b8916fe57b4534e628_ppc64le as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9@sha256:32ef9228f43a5d3bad7ce8916cd1170bd84573c03cb7e5f4e1c0da67813a21a6_arm64 as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9@sha256:75d039cf9da1facdf35deb724d82568cd23e2a059b6d5cb6944a39cca45c3cff_s390x as a component of Red Hat build of Keycloak 26.4; rhbk/keycloak-rhel9@sha256:967602076c4b0b80ab059470845af9656375deaf115c9f787b25514b5d3b6023_amd64 as a component of Red Hat build of Keycloak 26.4; 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 26.4.16; Red Hat build of Keycloak 26.6.7
    Red Hat Product Security ↗
  4. Vendor guidanceAuthoritative vendor guidance changed: removed vendor advisory: access.redhat.com/RHSA-2026:68276; removed vendor advisory: access.redhat.com/RHSA-2026:68277; 2 further removals.
    Before
    remediation: access.redhat.com/RHSA-2026:68276 · vendor advisory: access.redhat.com/RHSA-2026:68276 · vendor advisory: access.redhat.com/RHSA-2026:68277 · 2 more references
    After
    remediation: access.redhat.com/RHSA-2026:68276
    CNA ↗
  5. Vendor guidanceAuthoritative vendor guidance changed: added remediation: access.redhat.com/RHSA-2026:68276; added vendor advisory: access.redhat.com/RHSA-2026:68276; 3 further additions.
    Before
    no authoritative guidance recorded
    After
    remediation: access.redhat.com/RHSA-2026:68276 · vendor advisory: access.redhat.com/RHSA-2026:68276 · vendor advisory: access.redhat.com/RHSA-2026:68277 · 2 more references
    access.redhat.com ↗
  6. 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 26.4: 26.4-26 < *, 26.4.16-2 < *; Red Hat build of Keycloak 26.6: 26.6-20 < *, 26.6.7-3 < *
    CNA ↗
  7. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    access.redhat.com ↗
  8. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
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-2026-80828↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference · Red Hat RHSA-2026:68276↗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-2026-18212 · cve.blacktree.nl