diff --git a/.github/workflows/main.yaml b/.github/workflows/main.yaml
index 2f68432ba..aebd3b95d 100644
--- a/.github/workflows/main.yaml
+++ b/.github/workflows/main.yaml
@@ -36,8 +36,10 @@ jobs:
     name: Run Linter and Formatter
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - name: Lint pinned actions
+        run: bash tools/linter_actions_pinned.sh
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
           cache: 'pip' # caching pip dependencies
@@ -66,13 +68,13 @@ jobs:
         version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         folder: ["weaviate", "integration", "integration_embedded"]
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.version }}
           cache: 'pip' # caching pip dependencies
       - run: pip install -r requirements-devel.txt
-      - uses: jakebailey/pyright-action@v2
+      - uses: jakebailey/pyright-action@6cabc0f01c4994be48fd45cd9dbacdd6e1ee6e5e # v2
         with:
           version: 1.1.399
           working-directory: ${{ matrix.folder }}
@@ -86,8 +88,8 @@ jobs:
         version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         folder: ["test", "mock_tests"]
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.version }}
           cache: 'pip' # caching pip dependencies
@@ -96,7 +98,7 @@ jobs:
         run: pytest --cov -v --cov-report=term-missing --cov=weaviate --cov-report xml:coverage-${{ matrix.folder }}.xml ${{ matrix.folder }}
       - name: Archive code coverage results
         if: matrix.version == '3.10' && (github.ref_name != 'main')
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           name: coverage-report-${{ matrix.folder }}
           path: coverage-${{ matrix.folder }}.xml
@@ -110,8 +112,8 @@ jobs:
         grpc: ["1.59.5", "1.63.0", "1.65.0", "1.66.0", "1.68.0", "1.72.1", "1.73.0", "1.74.0"]
         protobuf: ["4.25.8", "5.26.0", "5.27.4", "5.28.3", "5.29.0", "6.30.0", "6.31.1", "6.32.0"]
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
           cache: 'pip' # caching pip dependencies
@@ -129,11 +131,11 @@ jobs:
         version: ["3.10", "3.11", "3.12", "3.13", "3.14"]
         optional_dependencies: [false]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           fetch-depth: 0
           fetch-tags: true
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.version }}
           cache: 'pip' # caching pip dependencies
@@ -145,7 +147,7 @@ jobs:
         run: pytest -v --cov --cov-report=term-missing --cov=weaviate --cov-report xml:coverage-integration-embedded.xml integration_embedded
       - name: Archive code coverage results
         if: matrix.version == '3.10' && (github.ref_name != 'main') && !github.event.pull_request.head.repo.fork
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           name: coverage-report-integration-embedded
           path: coverage-integration-embedded.xml
@@ -165,16 +167,16 @@ jobs:
         ]
         optional_dependencies: [false]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           fetch-depth: 0
           fetch-tags: true
-      - uses: actions/setup-python@v5
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: ${{ matrix.versions.py }}
           cache: 'pip' # caching pip dependencies
       - name: Login to Docker Hub
-        uses: docker/login-action@v3
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3
         if: ${{ !github.event.pull_request.head.repo.fork && github.triggering_actor != 'dependabot[bot]' }}
         with:
           username: ${{secrets.DOCKER_USERNAME}}
@@ -198,7 +200,7 @@ jobs:
         run: pytest -n auto --dist loadgroup -v --cov --cov-report=term-missing --cov=weaviate --cov-report xml:coverage-integration.xml integration
       - name: Archive code coverage results
         if: matrix.versions.py == '3.10' && (github.ref_name != 'main')
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           name: coverage-report-integration
           path: coverage-integration.xml
@@ -220,13 +222,13 @@ jobs:
         ]
         optional_dependencies: [false]
     steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
           cache: 'pip' # caching pip dependencies
       - name: Login to Docker Hub
-        uses: docker/login-action@v3
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3
         if: ${{ !github.event.pull_request.head.repo.fork && github.triggering_actor != 'dependabot[bot]' }}
         with:
           username: ${{secrets.DOCKER_USERNAME}}
@@ -245,25 +247,25 @@ jobs:
     runs-on: ubuntu-latest
     if: github.ref_name != 'main' && !github.event.pull_request.head.repo.fork
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
       - name: Download coverage artifacts mock
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: coverage-report-mock_tests
       - name: Download coverage artifacts unit
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: coverage-report-test
       - name: Download coverage integration
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: coverage-report-integration
       - name: Download coverage integration embedded
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: coverage-report-integration-embedded
       - name: Codecov
-        uses: codecov/codecov-action@v4
+        uses: codecov/codecov-action@b9fd7d16f6d7d1b5d2bec1a2887e65ceed900238 # v4
         with:
           fail_ci_if_error: true
           files: ./coverage-integration.xml, ./coverage-integration-embedded.xml, ./coverage-test.xml, ./coverage-mock_tests.xml
@@ -275,11 +277,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           fetch-depth: 0
       - name: Set up Python 3.11
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
           cache: 'pip' # caching pip dependencies
@@ -288,7 +290,7 @@ jobs:
       - name: Build a binary wheel
         run: python -m build
       - name: Create Wheel Artifacts
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
         with:
           path: "dist/*.whl"
           name: weaviate-python-client-wheel
@@ -315,17 +317,17 @@ jobs:
         ]
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           fetch-depth: 0
       - name: Login to Docker Hub
-        uses: docker/login-action@v3
+        uses: docker/login-action@c94ce9fb468520275223c153574b00df6fe4bcc9 # v3
         if: ${{ !github.event.pull_request.head.repo.fork && github.triggering_actor != 'dependabot[bot]' }}
         with:
           username: ${{secrets.DOCKER_USERNAME}}
           password: ${{secrets.DOCKER_PASSWORD}}
       - name: Download build artifact to append to release
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: weaviate-python-client-wheel
       - run: |
@@ -343,11 +345,11 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
         with:
           fetch-depth: 0
       - name: Set up Python 3.11
-        uses: actions/setup-python@v5
+        uses: actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065 # v5
         with:
           python-version: "3.11"
           cache: 'pip' # caching pip dependencies
@@ -357,7 +359,7 @@ jobs:
         run: python -m build
       - name: Publish distribution 📦 to PyPI on new tags
         if: startsWith(github.ref, 'refs/tags')
-        uses: pypa/gh-action-pypi-publish@release/v1
+        uses: pypa/gh-action-pypi-publish@cef221092ed1bacb1cc03d23a2d87d1d172e277b # release/v1
         with:
           verbose: true
           password: ${{ secrets.PYPI_API_TOKEN }}
@@ -369,12 +371,12 @@ jobs:
     needs: [build-and-publish]
     steps:
       - name: Download build artifact to append to release
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4
         with:
           name: weaviate-python-client-wheel
           path: dist
       - name: Release
-        uses: softprops/action-gh-release@v1
+        uses: softprops/action-gh-release@de2c0eb89ae2a093876385947365aca7b0e5f844 # v1
         with:
           generate_release_notes: true
           draft: true
diff --git a/.github/workflows/pr-security-lint.yaml b/.github/workflows/pr-security-lint.yaml
new file mode 100644
index 000000000..3dc27e534
--- /dev/null
+++ b/.github/workflows/pr-security-lint.yaml
@@ -0,0 +1,27 @@
+name: PR Security Lint
+
+on:
+  pull_request_target:
+    types: [opened, synchronize, reopened]
+
+# No permissions at workflow level — grant only what's needed at job level
+permissions: {}
+
+jobs:
+  hidden-unicode-check:
+    name: Check for hidden Unicode characters
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: read
+    steps:
+      - name: Checkout base branch
+        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          ref: ${{ github.event.pull_request.base.sha }}
+
+      - name: Check PR diff for hidden Unicode
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr diff ${{ github.event.pull_request.number }} | bash tools/linter_hidden_unicode.sh --stdin
diff --git a/tools/linter_actions_pinned.sh b/tools/linter_actions_pinned.sh
new file mode 100755
index 000000000..ebe39b378
--- /dev/null
+++ b/tools/linter_actions_pinned.sh
@@ -0,0 +1,49 @@
+#!/usr/bin/env bash
+# Lint GitHub Actions workflow files to ensure all external actions are pinned to SHA hashes.
+# Usage: bash tools/linter_actions_pinned.sh
+
+set -euo pipefail
+
+ERRORS=0
+
+for workflow in .github/workflows/*.yaml .github/workflows/*.yml; do
+    [ -f "$workflow" ] || continue
+
+    while IFS= read -r line; do
+        lineno=$(echo "$line" | cut -d: -f1)
+        content=$(echo "$line" | cut -d: -f2-)
+
+        # Extract the action reference (everything after "uses:")
+        action_ref=$(echo "$content" | sed -n 's/.*uses:[[:space:]]*//p' | xargs)
+
+        # Skip local actions (starting with ./)
+        if [[ "$action_ref" == ./* ]]; then
+            continue
+        fi
+
+        # Extract the version part (after @, before space or # comment)
+        version=$(echo "$action_ref" | sed -n 's/.*@\([^ #]*\).*/\1/p')
+
+        if [ -z "$version" ]; then
+            echo "::error file=${workflow},line=${lineno}::Action missing version pin: ${action_ref}"
+            ERRORS=$((ERRORS + 1))
+            continue
+        fi
+
+        # Check that the version is a 40-character hex SHA
+        if ! echo "$version" | grep -qE '^[0-9a-f]{40}$'; then
+            echo "::error file=${workflow},line=${lineno}::Action not pinned to SHA: ${action_ref} (version: ${version})"
+            ERRORS=$((ERRORS + 1))
+        fi
+    done < <(grep -n 'uses:' "$workflow")
+done
+
+if [ "$ERRORS" -gt 0 ]; then
+    echo ""
+    echo "ERROR: Found ${ERRORS} action(s) not pinned to a SHA hash."
+    echo "Replace tag references (e.g., @v5) with the full commit SHA (e.g., @93cb6ef...)"
+    echo "Preserve the tag as a comment: uses: actions/checkout@<SHA> # v5"
+    exit 1
+fi
+
+echo "All GitHub Actions are pinned to SHA hashes."
diff --git a/tools/linter_hidden_unicode.sh b/tools/linter_hidden_unicode.sh
new file mode 100755
index 000000000..c63a6edb2
--- /dev/null
+++ b/tools/linter_hidden_unicode.sh
@@ -0,0 +1,143 @@
+#!/usr/bin/env bash
+# Lint for hidden/invisible Unicode characters in diffs (trojan-source attack prevention).
+# Requires Perl (pre-installed on GitHub Actions Ubuntu runners).
+#
+# Usage:
+#   bash tools/linter_hidden_unicode.sh --stdin      # read diff from stdin (CI mode)
+#   bash tools/linter_hidden_unicode.sh <base-ref>   # diff against a base ref
+#   bash tools/linter_hidden_unicode.sh              # diff staged changes (git diff --cached)
+
+set -euo pipefail
+
+# Binary file extensions to skip
+BINARY_PATTERN='\.(png|jpg|jpeg|gif|ico|svg|woff2?|ttf|eot|otf|zip|tar|gz|bz2|xz|7z|rar|pdf|dll|exe|so|dylib|o|obj|class|jar|war|pyc|pyo|wasm|bin|dat|db|sqlite|nupkg|snupkg)$'
+
+get_diff() {
+    if [[ "${1:-}" == "--stdin" ]]; then
+        cat
+    elif [[ -n "${1:-}" ]]; then
+        # Validate ref argument to prevent command injection
+        if ! [[ "$1" =~ ^[a-zA-Z0-9._/-]+$ ]]; then
+            echo "ERROR: Invalid ref argument: $1" >&2
+            exit 1
+        fi
+        if ! git rev-parse --verify "$1" >/dev/null 2>&1; then
+            echo "ERROR: Git ref not found: $1" >&2
+            exit 2
+        fi
+        git diff "$1"
+    else
+        git diff --cached
+    fi
+}
+
+# Perl script that:
+# 1. Tracks current file from diff headers
+# 2. Skips binary files
+# 3. Scans only added lines (starting with +, excluding +++ headers)
+# 4. Detects ~30+ categories of invisible/suspicious Unicode characters
+PERL_SCRIPT='
+use utf8;
+use strict;
+use warnings;
+
+sub escape_property {
+    my ($s) = @_;
+    $s =~ s/%/%25/g;
+    $s =~ s/\r/%0D/g;
+    $s =~ s/\n/%0A/g;
+    $s =~ s/:/%3A/g;
+    $s =~ s/,/%2C/g;
+    return $s;
+}
+
+sub escape_message {
+    my ($s) = @_;
+    $s =~ s/%/%25/g;
+    $s =~ s/\r/%0D/g;
+    $s =~ s/\n/%0A/g;
+    return $s;
+}
+
+my $file = "";
+my $line_in_file = 0;
+my $errors = 0;
+my $in_binary = 0;
+my $binary_pattern = qr/'"$BINARY_PATTERN"'/i;
+
+while (<STDIN>) {
+    chomp;
+
+    # Track file from diff headers
+    if (/^\+\+\+ b\/(.+)$/) {
+        $file = $1;
+        $line_in_file = 0;
+        $in_binary = ($file =~ $binary_pattern) ? 1 : 0;
+        next;
+    }
+
+    # Skip binary file markers
+    if (/^Binary files/) {
+        $in_binary = 1;
+        next;
+    }
+
+    # Track hunk headers for line numbers
+    if (/^@@ -\d+(?:,\d+)? \+(\d+)/) {
+        $line_in_file = $1 - 1;
+        next;
+    }
+
+    # Count lines in the new file
+    if (/^\+/ || /^ /) {
+        $line_in_file++;
+    }
+
+    # Only scan added lines, skip binary files
+    next if $in_binary;
+    next unless /^\+/;
+    next if /^\+\+\+ (?:$|b\/|\/dev\/null)/;
+
+    # Remove the leading + for scanning
+    my $content = substr($_, 1);
+
+    # Check for suspicious invisible Unicode characters:
+    # - Bidi overrides and isolates (U+200E-200F, U+202A-202E, U+2066-2069)
+    # - Zero-width characters (U+200B-200D, U+2060)
+    # - Byte order mark mid-line (U+FEFF)
+    # - Soft hyphen (U+00AD)
+    # - Mongolian vowel separator (U+180E)
+    # - Combining grapheme joiner (U+034F)
+    # - Function application and invisible operators (U+2061-2064)
+    # - Hangul fillers (U+115F, U+1160, U+3164, U+FFA0)
+    # - Interlinear annotation (U+FFF9-FFFB)
+    # - Object replacement / replacement char (U+FFFC-FFFD) -- FFFD is sometimes legitimate
+    # - Unicode tag block (U+E0001, U+E0020-E007F)
+    # - Deprecated format chars (U+206A-206F)
+    if ($content =~ /([\x{00AD}\x{034F}\x{115F}\x{1160}\x{180E}\x{200B}-\x{200F}\x{202A}-\x{202E}\x{2060}-\x{2064}\x{2066}-\x{2069}\x{206A}-\x{206F}\x{3164}\x{FE00}-\x{FE0F}\x{FEFF}\x{FFA0}\x{FFF9}-\x{FFFB}\x{E0001}\x{E0020}-\x{E007F}])/) {
+        my $char = $1;
+        my $codepoint = sprintf("U+%04X", ord($char));
+        my $col = $-[1] + 1;
+
+        if ($ENV{GITHUB_ACTIONS}) {
+            my $efile = escape_property($file);
+            my $emsg = escape_message("Hidden Unicode character ${codepoint} found");
+            print "::error file=${efile},line=${line_in_file},col=${col}::${emsg}\n";
+        } else {
+            print "ERROR: $file:$line_in_file:$col - Hidden Unicode character $codepoint found\n";
+        }
+        $errors++;
+    }
+}
+
+if ($errors > 0) {
+    print "\nFound $errors hidden Unicode character(s) in added lines.\n";
+    print "These may indicate a trojan-source attack. See https://trojansource.codes/\n";
+    exit 1;
+} else {
+    print "No hidden Unicode characters detected.\n";
+    exit 0;
+}
+'
+
+get_diff "$@" | perl -CS -e "$PERL_SCRIPT"