RHSA-2026:26521 - Security Advisory

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