diff --git a/.github/workflows/ci_new.yml b/.github/workflows/ci_new.yml
index a1009e02b..1864411af 100644
--- a/.github/workflows/ci_new.yml
+++ b/.github/workflows/ci_new.yml
@@ -5,6 +5,97 @@ on:
   pull_request:
 
 jobs:
+  build-modsecurity-v3:
+    name: ModSecurity v3 (warn-only hardening build)
+    runs-on: ubuntu-24.04
+    env:
+      CC: gcc
+      CXX: g++
+      MODSECURITY_WARN_ONLY: "1"
+      COMMON_CC_OPT: "-O2 -pipe -fstack-protector-strong -fstack-clash-protection -ffunction-sections -fdata-sections -D_FORTIFY_SOURCE=2"
+      COMMON_LD_OPT: "-Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack -Wl,--as-needed -Wl,--gc-sections"
+      PIC_CC_OPT: "-fPIC"
+      MODSECURITY_CC_OPT: "-Wall -Wextra -Wformat -Wformat-security"
+      MODSECURITY_CXX_OPT: "-Wall -Wextra -Wformat -Wformat-security"
+      MODSECURITY_LD_OPT: "-Wl,-z,relro -Wl,-z,now -Wl,-z,noexecstack -Wl,--as-needed -Wl,--gc-sections"
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          fetch-depth: 0
+          submodules: recursive
+
+      - name: Detect latest Lua dev package
+        id: detect_lua
+        shell: bash
+        run: |
+          set -euo pipefail
+          sudo apt-get update -y -qq
+          CANDIDATES="$(apt-cache pkgnames | grep -E '^liblua[0-9]+\.[0-9]+-dev$' || true)"
+          [ -n "$CANDIDATES" ]
+          BEST_PKG="$(
+            printf '%s\n' "$CANDIDATES" \
+            | sed -E 's/^liblua([0-9]+\.[0-9]+)-dev$/\1 &/' \
+            | sort -V \
+            | tail -n1 \
+            | awk '{print $2}'
+          )"
+          [ -n "$BEST_PKG" ]
+          echo "lua_pkg=$BEST_PKG" >> "$GITHUB_OUTPUT"
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update -y -qq
+          sudo apt-get install -y \
+            autoconf automake libtool pkg-config bison flex \
+            libyajl-dev libcurl4-openssl-dev liblmdb-dev \
+            ${{ steps.detect_lua.outputs.lua_pkg }} \
+            libmaxminddb-dev libpcre2-dev libxml2-dev libfuzzy-dev
+
+      - name: Build preparation
+        run: ./build.sh
+
+      - name: Configure ModSecurity v3 flags
+        shell: bash
+        run: |
+          set -euo pipefail
+
+          C_WARNINGS="${MODSECURITY_CC_OPT}"
+          CXX_WARNINGS="${MODSECURITY_CXX_OPT}"
+
+          if [ "${MODSECURITY_WARN_ONLY:-0}" = "1" ]; then
+            C_WARNINGS="$(echo " ${C_WARNINGS} " | sed -E 's/[[:space:]]-Werror(=format-security)?[[:space:]]/ /g')"
+            CXX_WARNINGS="$(echo " ${CXX_WARNINGS} " | sed -E 's/[[:space:]]-Werror(=format-security)?[[:space:]]/ /g')"
+          fi
+
+          echo "CFLAGS=${COMMON_CC_OPT} ${PIC_CC_OPT} ${C_WARNINGS}" >> "$GITHUB_ENV"
+          echo "CXXFLAGS=${COMMON_CC_OPT} ${PIC_CC_OPT} ${CXX_WARNINGS}" >> "$GITHUB_ENV"
+          echo "CPPFLAGS=-D_FORTIFY_SOURCE=2" >> "$GITHUB_ENV"
+          echo "LDFLAGS=${COMMON_LD_OPT} ${MODSECURITY_LD_OPT}" >> "$GITHUB_ENV"
+
+      - name: Print toolchain and build configuration
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo "compiler version:"
+          ${CC} --version
+          echo
+          echo "linker version:"
+          ${CC} -Wl,--version | head -n1 || ld --version | head -n1
+          echo
+          echo "CFLAGS=${CFLAGS}"
+          echo "CXXFLAGS=${CXXFLAGS}"
+          echo "CPPFLAGS=${CPPFLAGS}"
+          echo "LDFLAGS=${LDFLAGS}"
+          echo "configure options: --enable-assertions=yes"
+          echo "MODSECURITY_WARN_ONLY=${MODSECURITY_WARN_ONLY}"
+          echo "Note: no LuaJIT rpath and no nginx/OpenResty-specific flags are used in this job."
+
+      - name: Configure
+        run: ./configure --enable-assertions=yes
+
+      - name: Build (verbose)
+        run: make -j "$(nproc)" V=1
+
   build-linux:
     name: Linux (${{ matrix.platform.label }}, ${{ matrix.compiler.label }}, ${{ matrix.configure.label }})