Red Hat Product Errata RHSA-2026:8850 - Security Advisory Issued: 2026-04-20 Updated: 2026-04-20 RHSA-2026:8850 - 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 8.4 Advanced Mission Critical Update Support and Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On. 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: thunderbird: Use-after-free in the JavaScript Engine component (CVE-2026-4701) firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149 (CVE-2026-4721) firefox: thunderbird: Privilege escalation in the Netmonitor component (CVE-2026-4717) firefox: thunderbird: Sandbox escape due to use-after-free in the Disability Access APIs component (CVE-2026-4688) firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component (CVE-2026-4706) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Web Codecs component (CVE-2026-4695) firefox: thunderbird: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component (CVE-2026-4689) firefox: thunderbird: JIT miscompilation in the JavaScript Engine: JIT component (CVE-2026-4698) firefox: thunderbird: Incorrect boundary conditions, uninitialized memory in the JavaScript Engine component (CVE-2026-4716) firefox: thunderbird: Race condition, use-after-free in the Graphics: WebRender component (CVE-2026-4684) firefox: thunderbird: Undefined behavior in the WebRTC: Signaling component (CVE-2026-4705) firefox: thunderbird: Uninitialized memory in the Graphics: Canvas2D component (CVE-2026-4715) firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component (CVE-2026-4685) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video component (CVE-2026-4714) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: GMP component (CVE-2026-4709) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video component (CVE-2026-4710) firefox: thunderbird: Information disclosure in the Widget: Cocoa component (CVE-2026-4712) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Web Codecs component (CVE-2026-4697) firefox: thunderbird: Incorrect boundary conditions in the Graphics component (CVE-2026-4713) firefox: thunderbird: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component (CVE-2026-4690) firefox: thunderbird: Use-after-free in the Widget: Cocoa component (CVE-2026-4711) firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component (CVE-2026-4686) firefox: thunderbird: Incorrect boundary conditions in the Graphics component (CVE-2026-4708) firefox: thunderbird: Use-after-free in the CSS Parsing and Computation component (CVE-2026-4691) firefox: thunderbird: Incorrect boundary conditions in the Layout: Text and Fonts component (CVE-2026-4699) firefox: thunderbird: Use-after-free in the Layout: Text and Fonts component (CVE-2026-4696) firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Playback component (CVE-2026-4693) firefox: thunderbird: Undefined behavior in the WebRTC: Signaling component (CVE-2026-4718) firefox: thunderbird: JIT miscompilation in the JavaScript Engine component (CVE-2026-4702) firefox: thunderbird: Incorrect boundary conditions in the Graphics: Text component (CVE-2026-4719) firefox: thunderbird: Incorrect boundary conditions, integer overflow in the Graphics component (CVE-2026-4694) firefox: thunderbird: Sandbox escape in the Responsive Design Mode component (CVE-2026-4692) firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149 (CVE-2026-4720) firefox: thunderbird: Mitigation bypass in the Networking: HTTP component (CVE-2026-4700) firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component (CVE-2026-4707) firefox: thunderbird: Denial-of-service in the WebRTC: Signaling component (CVE-2026-4704) firefox: thunderbird: Sandbox escape due to incorrect boundary conditions in the Telemetry component (CVE-2026-4687) thunderbird: Out of bounds read in IMAP parsing (CVE-2026-4371) thunderbird: Spoofing issue in Thunderbird (CVE-2026-3889) 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 Extension 8.4 x86_64 Red Hat Enterprise Linux Server - AUS 8.4 x86_64 Fixes BZ - 2450710 - CVE-2026-4701 firefox: thunderbird: Use-after-free in the JavaScript Engine component BZ - 2450711 - CVE-2026-4721 firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149 BZ - 2450712 - CVE-2026-4717 firefox: thunderbird: Privilege escalation in the Netmonitor component BZ - 2450713 - CVE-2026-4688 firefox: thunderbird: Sandbox escape due to use-after-free in the Disability Access APIs component BZ - 2450714 - CVE-2026-4706 firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component BZ - 2450715 - CVE-2026-4695 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Web Codecs component BZ - 2450718 - CVE-2026-4689 firefox: thunderbird: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component BZ - 2450719 - CVE-2026-4698 firefox: thunderbird: JIT miscompilation in the JavaScript Engine: JIT component BZ - 2450720 - CVE-2026-4716 firefox: thunderbird: Incorrect boundary conditions, uninitialized memory in the JavaScript Engine component BZ - 2450721 - CVE-2026-4684 firefox: thunderbird: Race condition, use-after-free in the Graphics: WebRender component BZ - 2450722 - CVE-2026-4705 firefox: thunderbird: Undefined behavior in the WebRTC: Signaling component BZ - 2450723 - CVE-2026-4715 firefox: thunderbird: Uninitialized memory in the Graphics: Canvas2D component BZ - 2450724 - CVE-2026-4685 firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component BZ - 2450725 - CVE-2026-4714 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video component BZ - 2450726 - CVE-2026-4709 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: GMP component BZ - 2450727 - CVE-2026-4710 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video component BZ - 2450728 - CVE-2026-4712 firefox: thunderbird: Information disclosure in the Widget: Cocoa component BZ - 2450729 - CVE-2026-4697 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Web Codecs component BZ - 2450730 - CVE-2026-4713 firefox: thunderbird: Incorrect boundary conditions in the Graphics component BZ - 2450732 - CVE-2026-4690 firefox: thunderbird: Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component BZ - 2450733 - CVE-2026-4711 firefox: thunderbird: Use-after-free in the Widget: Cocoa component BZ - 2450734 - CVE-2026-4686 firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component BZ - 2450735 - CVE-2026-4708 firefox: thunderbird: Incorrect boundary conditions in the Graphics component BZ - 2450738 - CVE-2026-4691 firefox: thunderbird: Use-after-free in the CSS Parsing and Computation component BZ - 2450739 - CVE-2026-4699 firefox: thunderbird: Incorrect boundary conditions in the Layout: Text and Fonts component BZ - 2450740 - CVE-2026-4696 firefox: thunderbird: Use-after-free in the Layout: Text and Fonts component BZ - 2450741 - CVE-2026-4693 firefox: thunderbird: Incorrect boundary conditions in the Audio/Video: Playback component BZ - 2450742 - CVE-2026-4718 firefox: thunderbird: Undefined behavior in the WebRTC: Signaling component BZ - 2450744 - CVE-2026-4702 firefox: thunderbird: JIT miscompilation in the JavaScript Engine component BZ - 2450746 - CVE-2026-4719 firefox: thunderbird: Incorrect boundary conditions in the Graphics: Text component BZ - 2450747 - CVE-2026-4694 firefox: thunderbird: Incorrect boundary conditions, integer overflow in the Graphics component BZ - 2450748 - CVE-2026-4692 firefox: thunderbird: Sandbox escape in the Responsive Design Mode component BZ - 2450751 - CVE-2026-4720 firefox: thunderbird: Memory safety bugs fixed in Firefox ESR 140.9, Thunderbird ESR 140.9, Firefox 149 and Thunderbird 149 BZ - 2450752 - CVE-2026-4700 firefox: thunderbird: Mitigation bypass in the Networking: HTTP component BZ - 2450755 - CVE-2026-4707 firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component BZ - 2450756 - CVE-2026-4704 firefox: thunderbird: Denial-of-service in the WebRTC: Signaling component BZ - 2450757 - CVE-2026-4687 firefox: thunderbird: Sandbox escape due to incorrect boundary conditions in the Telemetry component BZ - 2451001 - CVE-2026-4371 thunderbird: Out of bounds read in IMAP parsing BZ - 2451006 - CVE-2026-3889 thunderbird: Spoofing issue in Thunderbird CVEs CVE-2026-3889 CVE-2026-4371 CVE-2026-4684 CVE-2026-4685 CVE-2026-4686 CVE-2026-4687 CVE-2026-4688 CVE-2026-46