Red Hat Product Errata RHSA-2026:26521 - Security Advisory Issued: 2026-06-17 Updated: 2026-06-17 RHSA-2026:26521 - Security Advisory Overview Updated Packages Synopsis Important: thunderbird security update Type/Severity Security Advisory: Important Red Hat Lightspeed patch analysis Identify and remediate systems affected by this advisory. View affected systems Topic An update for thunderbird is now available for Red Hat Enterprise Linux 9.6 Extended Update Support. Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section. Description Mozilla Thunderbird is a standalone mail and newsgroup client. Security Fix(es): firefox: Incorrect boundary conditions in the JavaScript Engine: JIT component (CVE-2026-8388) firefox: Other issue in the JavaScript Engine component (CVE-2026-8391) firefox: Sandbox escape in the Profile Backup component (CVE-2026-8401) firefox: Integer overflow in the Networking: JAR component (CVE-2026-8956) firefox: Memory safety bugs fixed in Firefox ESR 115.36, Firefox ESR 140.11 and Firefox 151 (CVE-2026-8975) firefox: Privilege escalation in the DOM: Workers component (CVE-2026-8955) firefox: Denial-of-service due to invalid pointer in the Audio/Video: Web Codecs component (CVE-2026-8968) firefox: Incorrect boundary conditions, integer overflow in the Audio/Video component (CVE-2026-8954) firefox: Information disclosure, sandbox escape in the Security: Process Sandboxing component (CVE-2026-8958) firefox: Incorrect boundary conditions in the Audio/Video: Web Codecs component (CVE-2026-8946) firefox: Privilege escalation in the Security component (CVE-2026-8970) firefox: Same-origin policy bypass in the Networking: HTTP component (CVE-2026-8950) firefox: Memory safety bugs fixed in Firefox ESR 140.11 and Firefox 151 (CVE-2026-8974) firefox: Sandbox escape due to use-after-free in the Disability Access APIs component (CVE-2026-8953) firefox: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component (CVE-2026-8959) firefox: Spoofing issue in the Form Autofill component (CVE-2026-8961) firefox: Use-after-free in the DOM: Bindings (WebIDL) component (CVE-2026-8947) firefox: Mitigation bypass in the DOM: Security component (CVE-2026-8962) firefox: Privilege escalation in the Enterprise Policies component (CVE-2026-8957) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section. Solution For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Affected Products Red Hat Enterprise Linux for x86_64 - Extended Update Support 9.6 x86_64 Red Hat Enterprise Linux Server - AUS 9.6 x86_64 Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 9.6 s390x Red Hat Enterprise Linux for Power, little endian - Extended Update Support 9.6 ppc64le Red Hat Enterprise Linux for ARM 64 - Extended Update Support 9.6 aarch64 Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions 9.6 ppc64le Red Hat Enterprise Linux for x86_64 - Update Services for SAP Solutions 9.6 x86_64 Red Hat Enterprise Linux for ARM 64 - 4 years of updates 9.6 aarch64 Red Hat Enterprise Linux for IBM z Systems - 4 years of updates 9.6 s390x Red Hat Enterprise Linux for x86_64 - Extended Life Cycle 9.6 x86_64 Red Hat Enterprise Linux for ARM 64 - Extended Life Cycle 9.6 aarch64 Red Hat Enterprise Linux for Power, little endian - Extended Life Cycle 9.6 ppc64le Red Hat Enterprise Linux for IBM z Systems - Extended Life Cycle 9.6 s390x Fixes BZ - 2476469 - CVE-2026-8388 firefox: thunderbird: Incorrect boundary conditions in the JavaScript Engine: JIT component BZ - 2476475 - CVE-2026-8391 firefox: thunderbird: Other issue in the JavaScript Engine component BZ - 2476492 - CVE-2026-8401 firefox: thunderbird: Sandbox escape in the Profile Backup component BZ - 2479839 - CVE-2026-8956 firefox: Integer overflow in the Networking: JAR component BZ - 2479840 - CVE-2026-8975 firefox: Memory safety bugs fixed in Firefox ESR 115.36, Firefox ESR 140.11 and Firefox 151 BZ - 2479842 - CVE-2026-8955 firefox: thunderbird: Privilege escalation in the DOM: Workers component BZ - 2479846 - CVE-2026-8968 firefox: Denial-of-service due to invalid pointer in the Audio/Video: Web Codecs component BZ - 2479847 - CVE-2026-8954 firefox: Incorrect boundary conditions, integer overflow in the Audio/Video component BZ - 2479848 - CVE-2026-8958 firefox: Information disclosure, sandbox escape in the Security: Process Sandboxing component BZ - 2479849 - CVE-2026-8946 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Web Codecs component BZ - 2479852 - CVE-2026-8970 firefox: Privilege escalation in the Security component BZ - 2479853 - CVE-2026-8950 firefox: Same-origin policy bypass in the Networking: HTTP component BZ - 2479855 - CVE-2026-8974 firefox: Memory safety bugs fixed in Firefox ESR 140.11 and Firefox 151 BZ - 2479860 - CVE-2026-8953 firefox: Sandbox escape due to use-after-free in the Disability Access APIs component BZ - 2479861 - CVE-2026-8959 firefox: thunderbird: Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component BZ - 2479871 - CVE-2026-8961 firefox: Spoofing issue in the Form Autofill component BZ - 2479873 - CVE-2026-8947 firefox: thunderbird: Use-after-free in the DOM: Bindings (WebIDL) component BZ - 2479876 - CVE-2026-8962 firefox: Mitigation bypass in the DOM: Security component BZ - 2479880 - CVE-2026-8957 firefox: Privilege escalation in the Enterprise Policies component CVEs CVE-2026-8388 CVE-2026-8391 CVE-2026-8401 CVE-2026-8946 CVE-2026-8947 CVE-2026-8950 CVE-2026-8953 CVE-2026-8954 CVE-2026-8955 CVE-2026-8956 CVE-2026-8957 CVE-2026-8958 CVE-2026-8959 CVE-2026-8961 CVE-2026-8962 CVE-2026-8968 CVE-2026-8970 CVE-2026-8974 CVE-2026-8975 References https://access.redhat.com/security/updates/classification/#important Note: More recent versions of these packages may be available. Click a package name for more details. Red Hat Enterprise Linux for x86_64 - Extended Update Support 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 x86_64 thunderbird-140.11.0-1.el9_6.x86_64.rpm SHA-256: 6ce8c568b697c787a79fc5aeadcb116056ed0987f6a91917a7e2abab780da8a5 thunderbird-debuginfo-140.11.0-1.el9_6.x86_64.rpm SHA-256: 572e7057cfabe8854a2950a2137a5d33b6e4677cde56e2385966522d9edc28a9 thunderbird-debugsource-140.11.0-1.el9_6.x86_64.rpm SHA-256: 185382f2ea64e3992ceadbb435fafd1b9239fcad0d7c221b25cd0bb78cbe2b1f Red Hat Enterprise Linux Server - AUS 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 x86_64 thunderbird-140.11.0-1.el9_6.x86_64.rpm SHA-256: 6ce8c568b697c787a79fc5aeadcb116056ed0987f6a91917a7e2abab780da8a5 thunderbird-debuginfo-140.11.0-1.el9_6.x86_64.rpm SHA-256: 572e7057cfabe8854a2950a2137a5d33b6e4677cde56e2385966522d9edc28a9 thunderbird-debugsource-140.11.0-1.el9_6.x86_64.rpm SHA-256: 185382f2ea64e3992ceadbb435fafd1b9239fcad0d7c221b25cd0bb78cbe2b1f Red Hat Enterprise Linux for IBM z Systems - Extended Update Support 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 s390x thunderbird-140.11.0-1.el9_6.s390x.rpm SHA-256: c7b47b5019859b82c9426ac30b749cb1aadf4d32d96c1ddcc70f8af2d0e85fdb thunderbird-debuginfo-140.11.0-1.el9_6.s390x.rpm SHA-256: 809e31d849a607338ede60d92463fb6d7b743b413d35e55aee2a32570760675b thunderbird-debugsource-140.11.0-1.el9_6.s390x.rpm SHA-256: f90c173544a7d542850864535418bd8906916c2defed90dcaf7d3989cf983558 Red Hat Enterprise Linux for Power, little endian - Extended Update Support 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 ppc64le thunderbird-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 5eadffbe001a2e76e16d472fd1eba5bdc74fb10d714dbb5a4d8881c6314bdf12 thunderbird-debuginfo-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 88316e6e43c3e0d45016eb6e1e2947b776b11368e51112a127601c80c5b58806 thunderbird-debugsource-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 03b29cebc6e403c6b53450fe2f471682e93fda8b78a122439e32c36e7a222f53 Red Hat Enterprise Linux for ARM 64 - Extended Update Support 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 aarch64 thunderbird-140.11.0-1.el9_6.aarch64.rpm SHA-256: 5a9c08ea58ba7991551d9f6e0551c6339a9b867ca013338b0e46ed3fe3e5ab69 thunderbird-debuginfo-140.11.0-1.el9_6.aarch64.rpm SHA-256: 25b7651917ff8014e6165a8a641caa087713ae350ea9db24776c7c7e192e9bef thunderbird-debugsource-140.11.0-1.el9_6.aarch64.rpm SHA-256: a9b5c5cf3c2b85b0434299c73da1e1b9f3b689835a333fbbcd544ee0c2c8a3a3 Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 ppc64le thunderbird-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 5eadffbe001a2e76e16d472fd1eba5bdc74fb10d714dbb5a4d8881c6314bdf12 thunderbird-debuginfo-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 88316e6e43c3e0d45016eb6e1e2947b776b11368e51112a127601c80c5b58806 thunderbird-debugsource-140.11.0-1.el9_6.ppc64le.rpm SHA-256: 03b29cebc6e403c6b53450fe2f471682e93fda8b78a122439e32c36e7a222f53 Red Hat Enterprise Linux for x86_64 - Update Services for SAP Solutions 9.6 SRPM thunderbird-140.11.0-1.el9_6.src.rpm SHA-256: 44550d0b30b9204c5f551c4227cd2c1c3f380ba26be37a6485d880700c51f3d8 x86_64 thunderbird-140.11.0-1.el9_6.x86_64.rpm SHA-256: 6ce8c568b697c787a79fc5aeadcb116056ed0987f6a91917a7e2abab780da8a5 thunderbird-debugi