diff --git a/CVE-2021-29984.patch b/CVE-2021-29984.patch
new file mode 100644
index 0000000000000000000000000000000000000000..b833294a2d56afa23497ba5dc329366a16c0627b
--- /dev/null
+++ b/CVE-2021-29984.patch
@@ -0,0 +1,28 @@
+From aacfe50a8236d826f9ac615a3a2611fd1487997d Mon Sep 17 00:00:00 2001
+From: Jan de Mooij <jdemooij@mozilla.com>
+Date: Mon, 15 Jul 2024 16:46:36 +0800
+Subject: [PATCH] Bug 1720031 - Check for SetInitializedLength when reordering. r=iain
+
+Reference:https://hg.mozilla.org/integration/autoland/rev/7528462f1eef91beaf5a97c78c44b3c35b7f5cd1
+---
+ js/src/jit/InstructionReordering.cpp | 4 ++++
+ 1 file changed, 4 insertions(+)
+
+diff --git a/js/src/jit/InstructionReordering.cpp b/js/src/jit/InstructionReordering.cpp
+index 191fcb2..224bf0f 100644
+--- a/js/src/jit/InstructionReordering.cpp
++++ b/js/src/jit/InstructionReordering.cpp
+@@ -141,6 +141,10 @@ bool jit::ReorderInstructions(MIRGraph& graph) {
+         if (prev->isInterruptCheck()) {
+           break;
+         }
++        if (prev->isSetInitializedLength()) {
++          break;
++        }
++
+ 
+         // The instruction can't be moved before any of its uses.
+         bool isUse = false;
+-- 
+2.27.0
+
diff --git a/firefox.spec b/firefox.spec
index 19101ebbf497301c7cf3865ff480e07f1834d65b..2fd1ce105c88cba5cbac67c6b1ac7168101f2a5a 100644
--- a/firefox.spec
+++ b/firefox.spec
@@ -88,7 +88,7 @@
 Summary:             Mozilla Firefox Web browser
 Name:                firefox
 Version:             79.0
-Release:             26
+Release:             27
 URL:                 https://www.mozilla.org/firefox/
 License:             MPLv1.1 or GPLv2+ or LGPLv2+
 Source0:             https://archive.mozilla.org/pub/firefox/releases/%{version}/source/firefox-%{version}.source.tar.xz
@@ -207,6 +207,8 @@ Patch663:            CVE-2022-45406.patch
 Patch664:            CVE-2020-15675.patch
 Patch665:            CVE-2021-23972.patch
 Patch666:            CVE-2021-23954.patch
+Patch667:            CVE-2021-29984.patch
+
 %if %{?system_nss}
 BuildRequires:       pkgconfig(nspr) >= %{nspr_version} pkgconfig(nss) >= %{nss_version}
 BuildRequires:       nss-static >= %{nss_version}
@@ -407,6 +409,7 @@ tar -xf %{SOURCE3}
 %patch664 -p1
 %patch665 -p1
 %patch666 -p1
+%patch667 -p1
 
 %{__rm} -f .mozconfig
 %{__cp} %{SOURCE10} .mozconfig
@@ -855,6 +858,9 @@ gtk-update-icon-cache %{_datadir}/icons/hicolor &>/dev/null || :
 %endif
 
 %changelog
+* Mon Jul 15 2024 technology208 <technology@208suo.com> - 79.0-27
+- Fix CVE-2021-29984
+
 * Fri Jul 12 2024 technology208 <technology@208suo.com> - 79.0-26
 - Fix CVE-2020-15675,CVE-2021-23972,CVE-2021-23954