diff --git a/.github/codeql/codeql-config.yml b/.github/codeql/codeql-config.yml
new file mode 100644
index 0000000000..fb4cafd616
--- /dev/null
+++ b/.github/codeql/codeql-config.yml
@@ -0,0 +1,6 @@
+# Configuration for .github/workflows/codeql.yml: run only liboqs's own
+# queries. GitHub's stock suite already runs through CodeQL default setup.
+name: liboqs custom queries
+disable-default-queries: true
+queries:
+  - uses: ./.github/codeql/queries
diff --git a/.github/codeql/codeql-workspace.yml b/.github/codeql/codeql-workspace.yml
new file mode 100644
index 0000000000..32544f86ac
--- /dev/null
+++ b/.github/codeql/codeql-workspace.yml
@@ -0,0 +1,3 @@
+# Lets the test pack resolve the query pack locally.
+provide:
+  - "*/qlpack.yml"
diff --git a/.github/codeql/queries/openssl-return-check.ql b/.github/codeql/queries/openssl-return-check.ql
new file mode 100644
index 0000000000..ec3b29ad56
--- /dev/null
+++ b/.github/codeql/queries/openssl-return-check.ql
@@ -0,0 +1,25 @@
+/**
+ * @name Unchecked OpenSSL EVP return value
+ * @description Calls to OpenSSL EVP functions whose status code is discarded
+ *              silently ignore OpenSSL errors. Check the result, normally
+ *              with the OQS_OPENSSL_GUARD macro.
+ * @kind problem
+ * @problem.severity warning
+ * @precision high
+ * @id liboqs/openssl-unchecked-return
+ * @tags security
+ *       correctness
+ */
+
+import cpp
+
+from FunctionCall call, Function f
+where
+  f = call.getTarget() and
+  f.getName().matches("EVP%") and
+  not f.getUnspecifiedType() instanceof PointerType and
+  not f.getUnspecifiedType() instanceof VoidType and
+  // The status code is thrown away. Tested (e.g. by OQS_OPENSSL_GUARD), stored,
+  // or explicitly discarded with a (void) cast are all accepted.
+  call instanceof ExprInVoidContext
+select call, "Return value of " + f.getName() + "() is discarded; check it with OQS_OPENSSL_GUARD."
diff --git a/.github/codeql/queries/qlpack.yml b/.github/codeql/queries/qlpack.yml
new file mode 100644
index 0000000000..31e2c96c9a
--- /dev/null
+++ b/.github/codeql/queries/qlpack.yml
@@ -0,0 +1,4 @@
+name: liboqs/ci-queries
+version: 0.0.0
+dependencies:
+  codeql/cpp-all: "*"
diff --git a/.github/codeql/report_results.py b/.github/codeql/report_results.py
new file mode 100755
index 0000000000..005bf847dd
--- /dev/null
+++ b/.github/codeql/report_results.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: MIT
+
+import json
+import sys
+
+# Report the results of liboqs's custom CodeQL queries, failing if there are any.
+
+def escape(text):
+    # Characters with a special meaning in workflow command messages
+    return text.replace('%', '%25').replace('\r', '%0D').replace('\n', '%0A')
+
+
+def main(sarif_files):
+    count = 0
+    for sarif_file in sarif_files:
+        with open(sarif_file) as f:
+            sarif = json.load(f)
+        for run in sarif['runs']:
+            for result in run.get('results', []):
+                location = result['locations'][0]['physicalLocation']
+                path = location['artifactLocation']['uri']
+                line = location['region']['startLine']
+                message = f"[{result['ruleId']}] {result['message']['text']}"
+                print(f"::error file={path},line={line}::{escape(message)}")
+                count += 1
+
+    print(f"{count} result(s) from liboqs CodeQL queries")
+    return 1 if count else 0
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        sys.exit(__doc__)
+    sys.exit(main(sys.argv[1:]))
diff --git a/.github/codeql/test/openssl-return-check/openssl-return-check.expected b/.github/codeql/test/openssl-return-check/openssl-return-check.expected
new file mode 100644
index 0000000000..2e1a0b8af9
--- /dev/null
+++ b/.github/codeql/test/openssl-return-check/openssl-return-check.expected
@@ -0,0 +1,2 @@
+| test.c:22:2:22:18 | call to EVP_DigestInit_ex | Return value of EVP_DigestInit_ex() is discarded; check it with OQS_OPENSSL_GUARD. |
+| test.c:23:2:23:17 | call to EVP_DigestUpdate | Return value of EVP_DigestUpdate() is discarded; check it with OQS_OPENSSL_GUARD. |
diff --git a/.github/codeql/test/openssl-return-check/openssl-return-check.qlref b/.github/codeql/test/openssl-return-check/openssl-return-check.qlref
new file mode 100644
index 0000000000..196399338d
--- /dev/null
+++ b/.github/codeql/test/openssl-return-check/openssl-return-check.qlref
@@ -0,0 +1 @@
+openssl-return-check.ql
diff --git a/.github/codeql/test/openssl-return-check/test.c b/.github/codeql/test/openssl-return-check/test.c
new file mode 100644
index 0000000000..29de78b45d
--- /dev/null
+++ b/.github/codeql/test/openssl-return-check/test.c
@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: MIT
+// Test cases for queries/openssl-return-check.ql.
+// Self-contained: OpenSSL is stubbed so no headers are needed.
+
+typedef struct evp_md_ctx_st EVP_MD_CTX;
+typedef struct evp_md_st EVP_MD;
+
+int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, void *impl);
+int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned long cnt);
+EVP_MD_CTX *EVP_MD_CTX_new(void);
+void EVP_MD_CTX_free(EVP_MD_CTX *ctx);
+void exit(int status);
+
+#define OQS_OPENSSL_GUARD(x) \
+	do {                     \
+		if (1 != (x)) {      \
+			exit(1);         \
+		}                    \
+	} while (0)
+
+void bad_discarded(EVP_MD_CTX *ctx, const EVP_MD *md) {
+	EVP_DigestInit_ex(ctx, md, 0); // BAD
+	EVP_DigestUpdate(ctx, "x", 1); // BAD
+}
+
+void good_guarded(EVP_MD_CTX *ctx, const EVP_MD *md) {
+	OQS_OPENSSL_GUARD(EVP_DigestInit_ex(ctx, md, 0));
+}
+
+int good_tested(EVP_MD_CTX *ctx, const EVP_MD *md) {
+	if (EVP_DigestInit_ex(ctx, md, 0) != 1) {
+		return -1;
+	}
+	int ok = EVP_DigestUpdate(ctx, "x", 1);
+	return ok ? 0 : -1;
+}
+
+void good_explicitly_discarded(EVP_MD_CTX *ctx) {
+	(void)EVP_DigestUpdate(ctx, "x", 1);
+}
+
+void good_pointer_and_void_returns(void) {
+	EVP_MD_CTX *ctx = EVP_MD_CTX_new();
+	EVP_MD_CTX_free(ctx);
+}
diff --git a/.github/codeql/test/qlpack.yml b/.github/codeql/test/qlpack.yml
new file mode 100644
index 0000000000..86cb8d6c91
--- /dev/null
+++ b/.github/codeql/test/qlpack.yml
@@ -0,0 +1,5 @@
+name: liboqs/ci-queries-tests
+version: 0.0.0
+extractor: cpp
+dependencies:
+  liboqs/ci-queries: "*"
diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
new file mode 100644
index 0000000000..12d355676c
--- /dev/null
+++ b/.github/workflows/codeql.yml
@@ -0,0 +1,60 @@
+name: CodeQL custom queries
+
+permissions:
+  contents: read
+
+# Runs liboqs's own CodeQL queries (.github/codeql/queries) and fails if any of
+# them reports a result. Results are not uploaded to code scanning: this
+# repository uses CodeQL default setup, which rejects CodeQL SARIF uploads from
+# other workflows.
+on:
+  workflow_call:
+  workflow_dispatch:
+
+jobs:
+
+  query-tests:
+    name: CodeQL query unit tests
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # pin@v4
+      - name: Set up CodeQL CLI
+        id: init
+        uses: github/codeql-action/init@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        with:
+          languages: cpp
+          build-mode: none
+      - name: Run query unit tests
+        env:
+          CODEQL: ${{ steps.init.outputs.codeql-path }}
+        run: '"$CODEQL" test run .github/codeql/test'
+
+  analyze:
+    name: CodeQL custom queries
+    runs-on: ubuntu-latest
+    env:
+      # Works around a crash while finalizing the database (see #2415).
+      CODEQL_EXTRACTOR_CPP_TRAP_CACHING: false
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # pin@v4
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        with:
+          languages: cpp
+          build-mode: manual
+          config-file: ./.github/codeql/codeql-config.yml
+      - name: Build liboqs
+        # CodeQL only sees compiled code: build the default algorithms, with
+        # OpenSSL backing every primitive that supports it.
+        run: |
+          cmake -S . -B build -DOQS_USE_AES_OPENSSL=ON -DOQS_USE_SHA2_OPENSSL=ON -DOQS_USE_SHA3_OPENSSL=ON
+          cmake --build build --parallel "$(nproc)"
+      - name: Run CodeQL queries
+        uses: github/codeql-action/analyze@2892aa5e19bbd11bc0cff5427e3b750a04d9e3c2 # v4.38.2
+        with:
+          upload: false
+          output: sarif-results
+      - name: Report results
+        run: python3 .github/codeql/report_results.py sarif-results/*.sarif
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
index 9765399fec..04249f11d3 100644
--- a/.github/workflows/pr.yml
+++ b/.github/workflows/pr.yml
@@ -9,81 +9,8 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
+# TEST ONLY: trimmed to the CodeQL job for the fork test run. Drop this commit.
 jobs:
 
-  check-push-result:
-    name: Check if push CI passed for this commit
-    runs-on: ubuntu-latest
-    outputs:
-      skip_basic: ${{ steps.set_output.outputs.skip_basic }}
-    steps:
-      - name: Determine skip status
-        id: set_output
-        run: |
-          if [ "${{ github.event.pull_request.head.repo.fork }}" = "true" ]; then
-            echo "Fork PR - basic-checks cannot be skipped"
-            echo "skip_basic=false" >> $GITHUB_OUTPUT
-          else
-            SHA="${{ github.event.pull_request.head.sha }}"
-            RESPONSE=$(curl -s -H "Authorization: Bearer $GH_TOKEN" \
-              "https://api.github.com/repos/${{ github.repository }}/actions/runs?head_sha=$SHA&per_page=5")
-
-            # Pruefe ob "Push tests" Workflow mit conclusion=success existiert
-            if echo "$RESPONSE" | grep -q '"name": "Push tests"' && \
-               echo "$RESPONSE" | grep -q '"conclusion": "success"'; then
-              echo "Found successful Push tests for SHA $SHA - skipping basic-checks"
-              echo "skip_basic=true" >> $GITHUB_OUTPUT
-            else
-              echo "No successful Push tests found for SHA $SHA"
-              echo "skip_basic=false" >> $GITHUB_OUTPUT
-            fi
-          fi
-        env:
-          GH_TOKEN: ${{ github.token }}
-
-  basic-checks:
-    needs: check-push-result
-    if: needs.check-push-result.outputs.skip_basic == 'false'
-    concurrency:
-      group: basic-checks-${{ github.sha }}
-      cancel-in-progress: true
-    uses: ./.github/workflows/basic.yml
-    permissions:
-      contents: read
-      actions: write   # required to cancel the run on fail-fast (see basic.yml)
-
-  platform-tests:
-    needs: check-push-result
-    uses: ./.github/workflows/platforms.yml
-
-  code-coverage:
-    needs: check-push-result
-    if: needs.check-push-result.outputs.skip_basic == 'false'
-    uses: ./.github/workflows/code-coverage.yml
-    secrets: inherit
-
-  nix-full-build:
-    needs: check-push-result
-    if: needs.check-push-result.outputs.skip_basic == 'false' && (contains( github.event.pull_request.title, '[full tests]' ) || contains( github.event.pull_request.body, '[full tests]' ))
-    runs-on: ubuntu-latest
-    permissions:
-      contents: read
-    steps:
-      - uses: DeterminateSystems/nix-installer-action@3138316df39ed29be04236d7ffc686fa525866aa # v23
-      - name: Checkout code
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # pin@v4
-      - name: Check devShell
-        run: nix develop --command echo
-      - name: Check flake syntax
-        run: nix flake check --no-build
-      - name: Full flake build
-        run: nix build
-
-  scorecard:
-    needs: check-push-result
-    uses: ./.github/workflows/supplychain.yml
-    secrets: inherit
-    permissions:
-      contents: read
-      id-token: write
-      security-events: write
+  codeql:
+    uses: ./.github/workflows/codeql.yml
diff --git a/.github/workflows/push.yml b/.github/workflows/push.yml
index 2eb2db5bea..eb285fdcdd 100644
--- a/.github/workflows/push.yml
+++ b/.github/workflows/push.yml
@@ -5,7 +5,7 @@ permissions:
 
 on:
   push:
-    branches-ignore: 'main'
+    branches-ignore: ['main', 'feat/revived-codeql-openssl-return-check']  # TEST ONLY
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index f6a09cf283..eac650617b 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -119,3 +119,39 @@ If you feel like contributing but don't know what specific topic to work on,
 please check the [open issues tagged "good first issue" or "help wanted"](https://github.com/open-quantum-safe/liboqs/issues).
 
 You can also take a look at the [contribution wishlist](https://github.com/open-quantum-safe/liboqs/wiki/Contribution-wishlist) for more substantial contributions we are interested in.
+
+## Custom CodeQL queries
+
+There are two ways in which CodeQL runs in this repo: via GitHub's standard
+code scanning settings, and via `.github/workflows/codeql.yml`:
+- GitHub's standard scans are run via liboqs' repository code scanning settings.
+  Results appear as code scanning alerts in the repository's Security tab.
+- `.github/workflows/codeql.yml` runs liboqs's own CodeQL queries on every pull
+  request and fails if any of them reports a result. Each result is shown as an
+  error annotation on the pull request and in the job log. Its results are not uploaded 
+  to code scanning: while default setup is enabled, GitHub rejects CodeQL results uploaded 
+  by other workflows ([details](https://docs.github.com/en/code-security/reference/code-scanning/sarif-files/troubleshoot-sarif-uploads/default-setup-enabled)).
+  The workflow can also be run manually from the repository's Actions tab.
+
+The custom queries and their tests live in `.github/codeql/`:
+- `.github/codeql/queries/` holds the queries (e.g. `openssl-return-check.ql`,
+  which flags `EVP_*` calls whose status code is discarded instead of checked
+  with `OQS_OPENSSL_GUARD`)
+- `.github/codeql/test/<query-name>/` holds a unit test for each query: a small
+  C file with good and bad examples, a `.qlref` naming the query, and a
+  `.expected` file listing the results the query must report.
+
+The commands below need the CodeQL CLI: either install the GitHub CLI extension
+(`gh extension install github/gh-codeql`, then use `gh codeql` in place of
+`codeql`), or download a CodeQL bundle from the
+[github/codeql-action releases](https://github.com/github/codeql-action/releases).
+
+To add a query, add the `.ql` file and its test directory, then generate the
+`.expected` file and check that it lists exactly the bad examples:
+
+```bash
+codeql test run --learn .github/codeql/test
+```
+
+Run `codeql test run .github/codeql/test` (without `--learn`) to check that
+existing queries still behave as expected.