{"id":"CVE-2026-39823","title":"html/template: golang: Go html/template: Cross-Site Scripting via improper URL escaping in meta tag content (CVE-2026-39823)","summary":"A flaw was found in the `html/template` package of Go. A remote attacker could exploit this vulnerability by inserting ASCII whitespaces around the equals sign (`=`) within a URL's content attribute inside a `<meta>` tag. This improper esc…","severity":"medium","cvss":5.4,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N","cvssSource":"vendor","cwe":"CWE-79","vendor":"Red Hat","product":"Red Hat OpenShift Container Platform 4","affected":["assisted_installer_for_red_hat_openshift_container_platform 2","builds_for_red_hat_openshift","cert_manager_operator_for_red_hat_openshift","compliance_operator","confidential_compute_attestation","cryostat 4","custom_metric_autoscaler_operator_for_red_hat_openshift","deployment_validation_operator","external_secrets_operator_for_red_hat_openshift","file_integrity_operator","gatekeeper 3","logging_subsystem_for_red_hat_openshift","logical_volume_manager_storage","migration_toolkit_for_applications 8","migration_toolkit_for_containers","multiarch_tuning_operator","multicluster_engine_for_kubernetes","multicluster_global_hub","network_observability_operator","openshift_developer_tools_and_services","openshift_lightspeed","openshift_pipelines","openshift_serverless","openshift_service_mesh 2","openshift_service_mesh 3","power_monitoring_for_red_hat_openshift","3scale_api_management_platform 2","advanced_cluster_management_for_kubernetes 2","advanced_cluster_security 4","ansible_automation_platform 2","ceph_storage 5","ceph_storage 6","ceph_storage 7","ceph_storage 8","ceph_storage 9","certification_program_for_red_hat_enterprise_linux 9","connectivity_link 1","developer_hub","edge_manager 1","enterprise_linux 10"],"patched":["enterprise_linux_appstream_eus_v_10_0","enterprise_linux_appstream_v_10","enterprise_linux_appstream_v_8","enterprise_linux_appstream_e4s_v_9_2","enterprise_linux_appstream_e4s_v_9_4","enterprise_linux_appstream_eus_v_9_6","enterprise_linux_appstream_v_9","openshift_api_for_data_protection 1.6","hardened_images","openshift_distributed_tracing 3.10.2","multicluster_engine_for_kubernetes 2.11"],"published":"2026-05-07","updated":"2026-09-21","sourceUpdated":"2026-09-21T17:36:40+00:00","source":"CSAF","sourceUrl":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39823.json","references":[{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39823.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-39823"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2467811"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-39823"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-39823"},{"url":"https://go.dev/cl/769920"},{"url":"https://go.dev/issue/78913"},{"url":"https://groups.google.com/g/golang-announce/c/qcCIEXso47M"},{"url":"https://pkg.go.dev/vuln/GO-2026-4982"},{"url":"https://access.redhat.com/errata/RHSA-2026:49702"},{"url":"https://access.redhat.com/errata/RHSA-2026:22120"},{"url":"https://access.redhat.com/errata/RHSA-2026:22112"},{"url":"https://access.redhat.com/errata/RHSA-2026:61253"},{"url":"https://access.redhat.com/errata/RHSA-2026:57649"},{"url":"https://access.redhat.com/errata/RHSA-2026:49712"},{"url":"https://access.redhat.com/errata/RHSA-2026:22121"},{"url":"https://access.redhat.com/errata/RHSA-2026:43692"},{"url":"https://access.redhat.com/errata/RHSA-2026:23262"},{"url":"https://access.redhat.com/errata/RHSA-2026:23264"},{"url":"https://access.redhat.com/errata/RHSA-2026:50205"},{"url":"https://access.redhat.com/errata/RHSA-2026:57194"}],"tags":["csaf","vex","red-hat","osv","go"],"epss":0.00333,"epssPercentile":0.23711,"aliases":["GO-2026-4982","BIT-golang-2026-39823"],"ecosystem":"go","ingestedAt":"2026-08-26T19:27:02.507Z","slug":"CVE-2026-39823","body":"## Overview\n\nA flaw was found in the `html/template` package of Go. A remote attacker could exploit this vulnerability by inserting ASCII whitespaces around the equals sign (`=`) within a URL's content attribute inside a `<meta>` tag. This improper escaping could lead to Cross-Site Scripting (XSS), allowing the attacker to execute malicious scripts in the user's browser.\n\n## Vendor advisories\n\n- **RHSA-2026:49702** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v. 10.0) · released 2026-08-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:49702)\n- **RHSA-2026:22120** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10) · released 2026-06-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:22120)\n- **RHSA-2026:22112** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8) · released 2026-06-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:22112)\n- **RHSA-2026:61253** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream E4S (v.9.2) · released 2026-08-31 · [advisory](https://access.redhat.com/errata/RHSA-2026:61253)\n- **RHSA-2026:57649** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream E4S (v.9.4) · released 2026-08-20 · [advisory](https://access.redhat.com/errata/RHSA-2026:57649)\n- **RHSA-2026:49712** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream EUS (v.9.6) · released 2026-08-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:49712)\n- **RHSA-2026:22121** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9) · released 2026-06-01 · [advisory](https://access.redhat.com/errata/RHSA-2026:22121)\n- **RHSA-2026:43692** · Red Hat · fixed in: OpenShift API for Data Protection 1.6 · released 2026-07-22 · [advisory](https://access.redhat.com/errata/RHSA-2026:43692)\n- **RHSA-2026:23262** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-06-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:23262)\n- **RHSA-2026:23264** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-06-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:23264)\n- **RHSA-2026:50205** · Red Hat · fixed in: Red Hat OpenShift distributed tracing 3.10.2 · released 2026-08-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:50205)\n- **Red Hat VEX** · Moderate · affected: Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, Compliance Operator, Confidential Compute Attestation, Cryostat 4, … · no fix planned: Red Hat Enterprise Linux 10, Assisted Installer for Red Hat OpenShift Container Platform 2, Builds for Red Hat OpenShift, cert-manager Operator for Red Hat OpenShift, … · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-39823.json)\n\n**html/template: golang: Go html/template: Cross-Site Scripting via improper URL escaping in meta tag content** — rated Moderate by Red Hat. Released 2026-05-07, updated 2026-09-21.\n\nAffected:\n\n- Assisted Installer for Red Hat OpenShift Container Platform 2\n- Builds for Red Hat OpenShift\n- cert-manager Operator for Red Hat OpenShift\n- Compliance Operator\n- Confidential Compute Attestation\n- Cryostat 4\n- Custom Metric Autoscaler operator for Red Hat Openshift\n- Deployment Validation Operator\n- External Secrets Operator for Red Hat OpenShift\n- File Integrity Operator\n- Gatekeeper 3\n- Logging Subsystem for Red Hat OpenShift\n- Logical Volume Manager Storage\n- Migration Toolkit for Applications 8\n- Migration Toolkit for Containers\n- Multiarch Tuning Operator\n- Multicluster Engine for Kubernetes\n- Multicluster Global Hub\n- Network Observability Operator\n- OpenShift Developer Tools and Services\n- OpenShift Lightspeed\n- OpenShift Pipelines\n- OpenShift Serverless\n- OpenShift Service Mesh 2\n- OpenShift Service Mesh 3\n- Power monitoring for Red Hat OpenShift\n- Red Hat 3scale API Management Platform 2\n- Red Hat Advanced Cluster Management for Kubernetes 2\n- Red Hat Advanced Cluster Security 4\n- Red Hat Ansible Automation Platform 2\n- Red Hat Ceph Storage 5\n- Red Hat Ceph Storage 6\n- Red Hat Ceph Storage 7\n- Red Hat Ceph Storage 8\n- Red Hat Ceph Storage 9\n- Red Hat Certification Program for Red Hat Enterprise Linux 9\n- Red Hat Connectivity Link 1\n- Red Hat Developer Hub\n- Red Hat Edge Manager 1\n- Red Hat Enterprise Linux 10\n\nFixed:\n\n- Red Hat Enterprise Linux AppStream EUS (v. 10.0)\n- Red Hat Enterprise Linux AppStream (v. 10)\n- Red Hat Enterprise Linux AppStream (v. 8)\n- Red Hat Enterprise Linux AppStream E4S (v.9.2)\n- Red Hat Enterprise Linux AppStream E4S (v.9.4)\n- Red Hat Enterprise Linux AppStream EUS (v.9.6)\n- Red Hat Enterprise Linux AppStream (v. 9)\n- OpenShift API for Data Protection 1.6\n- Red Hat Hardened Images\n- Red Hat OpenShift distributed tracing 3.10.2\n- multicluster engine for Kubernetes 2.11\n\nNo fix planned:\n\n- Red Hat Enterprise Linux 10\n- Assisted Installer for Red Hat OpenShift Container Platform 2\n- Builds for Red Hat OpenShift\n- cert-manager Operator for Red Hat OpenShift\n- Compliance Operator\n- Confidential Compute Attestation\n- Cryostat 4\n- Custom Metric Autoscaler operator for Red Hat Openshift\n- Deployment Validation Operator\n- External Secrets Operator for Red Hat OpenShift\n- File Integrity Operator\n- Gatekeeper 3\n- Logging Subsystem for Red Hat OpenShift\n- Logical Volume Manager Storage\n- Migration Toolkit for Applications 8\n- Migration Toolkit for Containers\n- Multiarch Tuning Operator\n- Multicluster Engine for Kubernetes\n- Multicluster Global Hub\n- Network Observability Operator\n- OpenShift Developer Tools and Services\n- OpenShift Lightspeed\n- OpenShift Pipelines\n- OpenShift Serverless\n- OpenShift Service Mesh 2\n- OpenShift Service Mesh 3\n- Power monitoring for Red Hat OpenShift\n- Red Hat 3scale API Management Platform 2\n- Red Hat Advanced Cluster Management for Kubernetes 2\n- Red Hat Advanced Cluster Security 4\n- Red Hat Ansible Automation Platform 2\n- Red Hat Ceph Storage 5\n- Red Hat Ceph Storage 6\n- Red Hat Ceph Storage 7\n- Red Hat Ceph Storage 8\n- Red Hat Ceph Storage 9\n- Red Hat Certification Program for Red Hat Enterprise Linux 9\n- Red Hat Connectivity Link 1\n- Red Hat Developer Hub\n- Red Hat Edge Manager 1\n\nNot affected:\n\n- OpenShift API for Data Protection 1.6\n- Red Hat OpenShift distributed tracing 3.10.2\n- multicluster engine for Kubernetes 2.11\n- Red Hat OpenShift Container Platform 4\n\n## Remediation\n\nFor details on how to apply this update, which includes the changes described in this advisory, refer to:\n\nhttps://access.redhat.com/articles/11258 https://access.redhat.com/errata/RHSA-2026:49702\nFor details on how to apply this update, which includes the changes described in this advisory, refer to:\n\nhttps://access.redhat.com/articles/11258 https://access.redhat.com/errata/RHSA-2026:22120\nFor details on how to apply this update, which includes the changes described in this advisory, refer to:\n\nhttps://access.redhat.com/articles/11258 https://access.redhat.com/errata/RHSA-2026:22112\n\nWorkarounds / mitigations:\n\n- Ensure that user-supplied URLs are validated and sanitized before being passed to Go's `html/template` package for rendering in HTML meta tag content attributes. Avoid rendering untrusted URL data directly in meta tag content attributes.\n\n## Package advisory (CVE-2026-39823)\n\nAffected packages:\n\n- `stdlib >= 1.26.0-0, < 1.26.3`\n\nPatched in:\n\n- `stdlib 1.26.3`\n\nSource: https://osv.dev/vulnerability/GO-2026-4982","depth":"sunlit","depthScore":30,"depthScoreParts":{"impact":29.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":5152,"id":"CVE-2026-39823","ts":1788887250913,"field":"cvss","old":null,"new":"5.4"},{"seq":5151,"id":"CVE-2026-39823","ts":1788887250913,"field":"severity","old":"none","new":"medium"},{"seq":4035,"id":"CVE-2026-39823","ts":1788886366823,"field":"cvss","old":"5.4","new":null},{"seq":4034,"id":"CVE-2026-39823","ts":1788886366823,"field":"severity","old":"medium","new":"none"},{"seq":3157,"id":"CVE-2026-39823","ts":1788883133124,"field":"cvss","old":null,"new":"5.4"},{"seq":3156,"id":"CVE-2026-39823","ts":1788883133124,"field":"severity","old":"none","new":"medium"}]}