diff --git a/.github/scripts/install-musl-build-tools.sh b/.github/scripts/install-musl-build-tools.sh
index 49035f5391..e4c6683d0e 100644
--- a/.github/scripts/install-musl-build-tools.sh
+++ b/.github/scripts/install-musl-build-tools.sh
@@ -150,9 +150,7 @@ for arg in "\$@"; do
   args+=("\${arg}")
 done
 
-# Zig enables UBSan for debug C builds by default. Rust links these objects
-# without Zig's sanitizer runtime, so keep native dependencies uninstrumented.
-exec "${zig_bin}" cc -target "${zig_target}" "\${args[@]}" -fno-sanitize=undefined
+exec "${zig_bin}" cc -target "${zig_target}" "\${args[@]}"
 EOF
   cat >"${cxx}" <<EOF
 #!/usr/bin/env bash
@@ -209,9 +207,7 @@ for arg in "\$@"; do
   args+=("\${arg}")
 done
 
-# Zig enables UBSan for debug C++ builds by default. Rust links these objects
-# without Zig's sanitizer runtime, so keep native dependencies uninstrumented.
-exec "${zig_bin}" c++ -target "${zig_target}" "\${args[@]}" -fno-sanitize=undefined
+exec "${zig_bin}" c++ -target "${zig_target}" "\${args[@]}"
 EOF
   chmod +x "${cc}" "${cxx}"
 
@@ -274,11 +270,6 @@ echo "PKG_CONFIG_PATH=${pkg_config_path}" >> "$GITHUB_ENV"
 pkg_config_path_var="PKG_CONFIG_PATH_${TARGET}"
 pkg_config_path_var="${pkg_config_path_var//-/_}"
 echo "${pkg_config_path_var}=${libcap_pkgconfig_dir}" >> "$GITHUB_ENV"
-pkg_config_libdir_var="PKG_CONFIG_LIBDIR_${TARGET}"
-pkg_config_libdir_var="${pkg_config_libdir_var//-/_}"
-# Do not let musl cross-builds resolve native libraries from the host glibc
-# pkg-config directories. libcap is the only target package provided here.
-echo "${pkg_config_libdir_var}=${libcap_pkgconfig_dir}" >> "$GITHUB_ENV"
 
 if [[ -n "${sysroot}" && "${sysroot}" != "/" ]]; then
   echo "PKG_CONFIG_SYSROOT_DIR=${sysroot}" >> "$GITHUB_ENV"
diff --git a/.github/workflows/rust-ci-full.yml b/.github/workflows/rust-ci-full.yml
index 3031cb6853..702ad12dbb 100644
--- a/.github/workflows/rust-ci-full.yml
+++ b/.github/workflows/rust-ci-full.yml
@@ -260,7 +260,11 @@ jobs:
           set -euo pipefail
           if command -v apt-get >/dev/null 2>&1; then
             sudo apt-get update -y
-            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends pkg-config libcap-dev
+            packages=(pkg-config libcap-dev)
+            if [[ "${{ matrix.target }}" == 'x86_64-unknown-linux-musl' || "${{ matrix.target }}" == 'aarch64-unknown-linux-musl' ]]; then
+              packages+=(libubsan1)
+            fi
+            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends "${packages[@]}"
           fi
       - uses: dtolnay/rust-toolchain@e081816240890017053eacbb1bdf337761dc5582 # 1.95.0
         with:
@@ -344,6 +348,14 @@ jobs:
             sccache-${{ matrix.runner }}-${{ matrix.target }}-${{ matrix.profile }}-${{ steps.lockhash.outputs.hash }}-
             sccache-${{ matrix.runner }}-${{ matrix.target }}-${{ matrix.profile }}-
 
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Disable sccache wrapper (musl)
+        shell: bash
+        run: |
+          set -euo pipefail
+          echo "RUSTC_WRAPPER=" >> "$GITHUB_ENV"
+          echo "RUSTC_WORKSPACE_WRAPPER=" >> "$GITHUB_ENV"
+
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
         name: Prepare APT cache directories (musl)
         shell: bash
@@ -377,6 +389,58 @@ jobs:
         shell: bash
         run: bash "${GITHUB_WORKSPACE}/.github/scripts/install-musl-build-tools.sh"
 
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Configure rustc UBSan wrapper (musl host)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ubsan=""
+          if command -v ldconfig >/dev/null 2>&1; then
+            ubsan="$(ldconfig -p | grep -m1 'libubsan\.so\.1' | sed -E 's/.*=> (.*)$/\1/')"
+          fi
+          wrapper_root="${RUNNER_TEMP:-/tmp}"
+          wrapper="${wrapper_root}/rustc-ubsan-wrapper"
+          cat > "${wrapper}" <<EOF
+          #!/usr/bin/env bash
+          set -euo pipefail
+          if [[ -n "${ubsan}" ]]; then
+            export LD_PRELOAD="${ubsan}\${LD_PRELOAD:+:\${LD_PRELOAD}}"
+          fi
+          exec "\$1" "\${@:2}"
+          EOF
+          chmod +x "${wrapper}"
+          echo "RUSTC_WRAPPER=${wrapper}" >> "$GITHUB_ENV"
+          echo "RUSTC_WORKSPACE_WRAPPER=" >> "$GITHUB_ENV"
+
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Clear sanitizer flags (musl)
+        shell: bash
+        run: |
+          set -euo pipefail
+          # Clear global Rust flags so host/proc-macro builds don't pull in UBSan.
+          echo "RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_ENCODED_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "RUSTDOCFLAGS=" >> "$GITHUB_ENV"
+          # Override any runner-level Cargo config rustflags as well.
+          echo "CARGO_BUILD_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
+
+          sanitize_flags() {
+            local input="$1"
+            input="${input//-fsanitize=undefined/}"
+            input="${input//-fno-sanitize-recover=undefined/}"
+            input="${input//-fno-sanitize-trap=undefined/}"
+            echo "$input"
+          }
+
+          cflags="$(sanitize_flags "${CFLAGS-}")"
+          cxxflags="$(sanitize_flags "${CXXFLAGS-}")"
+          echo "CFLAGS=${cflags}" >> "$GITHUB_ENV"
+          echo "CXXFLAGS=${cxxflags}" >> "$GITHUB_ENV"
+
       - if: ${{ !contains(matrix.target, 'windows') }}
         name: Configure rusty_v8 artifact overrides and verify checksums
         uses: ./.github/actions/setup-rusty-v8
diff --git a/.github/workflows/rust-release.yml b/.github/workflows/rust-release.yml
index 07a2e87ef2..eaf886cd01 100644
--- a/.github/workflows/rust-release.yml
+++ b/.github/workflows/rust-release.yml
@@ -245,6 +245,15 @@ jobs:
           set -euo pipefail
           sudo apt-get update -y
           sudo DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends pkg-config libcap-dev
+      - name: Install UBSan runtime (musl)
+        if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl' }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          if command -v apt-get >/dev/null 2>&1; then
+            sudo apt-get update -y
+            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y libubsan1
+          fi
       - uses: dtolnay/rust-toolchain@e081816240890017053eacbb1bdf337761dc5582 # 1.95.0
         with:
           targets: ${{ matrix.target }}
@@ -274,7 +283,30 @@ jobs:
         run: bash "${GITHUB_WORKSPACE}/.github/scripts/install-musl-build-tools.sh"
 
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
-        name: Disable aws-lc jitter entropy (musl)
+        name: Configure rustc UBSan wrapper (musl host)
+        shell: bash
+        run: |
+          set -euo pipefail
+          ubsan=""
+          if command -v ldconfig >/dev/null 2>&1; then
+            ubsan="$(ldconfig -p | grep -m1 'libubsan\.so\.1' | sed -E 's/.*=> (.*)$/\1/')"
+          fi
+          wrapper_root="${RUNNER_TEMP:-/tmp}"
+          wrapper="${wrapper_root}/rustc-ubsan-wrapper"
+          cat > "${wrapper}" <<EOF
+          #!/usr/bin/env bash
+          set -euo pipefail
+          if [[ -n "${ubsan}" ]]; then
+            export LD_PRELOAD="${ubsan}\${LD_PRELOAD:+:\${LD_PRELOAD}}"
+          fi
+          exec "\$1" "\${@:2}"
+          EOF
+          chmod +x "${wrapper}"
+          echo "RUSTC_WRAPPER=${wrapper}" >> "$GITHUB_ENV"
+          echo "RUSTC_WORKSPACE_WRAPPER=" >> "$GITHUB_ENV"
+
+      - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
+        name: Clear sanitizer flags (musl)
         shell: bash
         run: |
           set -euo pipefail
@@ -284,6 +316,30 @@ jobs:
           target_no_jitter="${target_no_jitter//-/_}"
           echo "${target_no_jitter}=1" >> "$GITHUB_ENV"
 
+          # Clear global Rust flags so host/proc-macro builds don't pull in UBSan.
+          echo "RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_ENCODED_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "RUSTDOCFLAGS=" >> "$GITHUB_ENV"
+          # Override any runner-level Cargo config rustflags as well.
+          echo "CARGO_BUILD_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
+          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
+
+          sanitize_flags() {
+            local input="$1"
+            input="${input//-fsanitize=undefined/}"
+            input="${input//-fno-sanitize-recover=undefined/}"
+            input="${input//-fno-sanitize-trap=undefined/}"
+            echo "$input"
+          }
+
+          cflags="$(sanitize_flags "${CFLAGS-}")"
+          cxxflags="$(sanitize_flags "${CXXFLAGS-}")"
+          echo "CFLAGS=${cflags}" >> "$GITHUB_ENV"
+          echo "CXXFLAGS=${cxxflags}" >> "$GITHUB_ENV"
+
       - name: Configure rusty_v8 artifact overrides and verify checksums
         uses: ./.github/actions/setup-rusty-v8
         with: