python · hugovk · Jan 16, 2026 · Jan 12, 2026 · Jan 12, 2026 · Jan 12, 2026
@@ -641,45 +641,44 @@ jobs:
         run: |
           "$BUILD_DIR/cross-python/bin/python3" -m test test_sysconfig test_site test_embed
 
-  # CIFuzz job based on https://google.github.io/oss-fuzz/getting-started/continuous-integration/
   cifuzz:
     name: CIFuzz
-    runs-on: ubuntu-latest
-    timeout-minutes: 60
     needs: build-context
-    if: needs.build-context.outputs.run-ci-fuzz == 'true'
+    if: >-
+      (
+        needs.build-context.outputs.run-ci-fuzz == 'true'
+        || needs.build-context.outputs.run-ci-fuzz-stdlib == 'true'
+      )
     permissions:
       security-events: write
     strategy:
       fail-fast: false
       matrix:
-        sanitizer: [address, undefined, memory]
-    steps:
-      - name: Build fuzzers (${{ matrix.sanitizer }})
-        id: build
-        uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
-        with:
-          oss-fuzz-project-name: cpython3
-          sanitizer: ${{ matrix.sanitizer }}
-      - name: Run fuzzers (${{ matrix.sanitizer }})
-        uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
-        with:
-          fuzz-seconds: 600
-          oss-fuzz-project-name: cpython3
-          output-sarif: true
-          sanitizer: ${{ matrix.sanitizer }}
-      - name: Upload crash
-        if: failure() && steps.build.outcome == 'success'
-        uses: actions/upload-artifact@v6
-        with:
-          name: ${{ matrix.sanitizer }}-artifacts
-          path: ./out/artifacts
-      - name: Upload SARIF
-        if: always() && steps.build.outcome == 'success'
-        uses: github/codeql-action/upload-sarif@v4
-        with:
-          sarif_file: cifuzz-sarif/results.sarif
-          checkout_path: cifuzz-sarif
+        sanitizer:
+        - address
+        - undefined
+        - memory
+        oss-fuzz-project-name:
+        - cpython3
+        - python3-libraries
+        exclude:
+        - oss-fuzz-project-name: >-
+            ${{
+              needs.build-context.outputs.run-ci-fuzz == 'true'
+              && ''
+              || 'cpython3'
+            }}
+        - oss-fuzz-project-name: >-
+            ${{
+              needs.build-context.outputs.run-ci-fuzz-stdlib == 'true'
+              && ''
+              || 'python3-libraries'
+            }}
+    uses: ./.github/workflows/reusable-cifuzz.yml
+    with:
+      oss-fuzz-project-name: ${{ matrix.oss-fuzz-project-name }}
+      sanitizer: ${{ matrix.sanitizer }}
+      timeout-minutes: 60
 
   all-required-green:  # This job does nothing and is only used for the branch protection
     name: All required checks pass
@@ -735,6 +734,7 @@ jobs:
           }}
           ${{ !fromJSON(needs.build-context.outputs.run-windows-tests) && 'build-windows,' || '' }}
           ${{ !fromJSON(needs.build-context.outputs.run-ci-fuzz) && 'cifuzz,' || '' }}
+          ${{ !fromJSON(needs.build-context.outputs.run-ci-fuzz-stdlib) && 'cifuzz,' || '' }}
           ${{ !fromJSON(needs.build-context.outputs.run-macos) && 'build-macos,' || '' }}
           ${{
             !fromJSON(needs.build-context.outputs.run-ubuntu)

@@ -0,0 +1,51 @@
+# CIFuzz job based on https://google.github.io/oss-fuzz/getting-started/continuous-integration/
+name: Reusable CIFuzz
+
+on:
+  workflow_call:
+    inputs:
+      oss-fuzz-project-name:
+        description: OSS-Fuzz project name
+        required: true
+        type: string
+      sanitizer:
+        description: OSS-Fuzz sanitizer
+        required: true
+        type: string
+      timeout-minutes:
+        description: Timeout in minutes for the action
+        required: false
+        default: 60
+        type: number
+
+jobs:
+  cifuzz:
+    name: CIFuzz
+    runs-on: ubuntu-latest
+    timeout-minutes: ${{ inputs.timeout-minutes }}
+    steps:
+      - name: Build fuzzers (${{ inputs.sanitizer }})
+        id: build
+        uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
+        with:
+          oss-fuzz-project-name: ${{ inputs.oss-fuzz-project-name }}
+          sanitizer: ${{ inputs.sanitizer }}
+      - name: Run fuzzers (${{ inputs.sanitizer }})
+        uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+        with:
+          fuzz-seconds: 600
+          oss-fuzz-project-name: ${{ inputs.oss-fuzz-project-name }}
+          output-sarif: true
+          sanitizer: ${{ inputs.sanitizer }}
+      - name: Upload crash
+        if: failure() && steps.build.outcome == 'success'
+        uses: actions/upload-artifact@v6
+        with:
+          name: ${{ inputs.sanitizer }}-artifacts
+          path: ./out/artifacts
+      - name: Upload SARIF
+        if: always() && steps.build.outcome == 'success'
+        uses: github/codeql-action/upload-sarif@v4
+        with:
+          sarif_file: cifuzz-sarif/results.sarif
+          checkout_path: cifuzz-sarif
@@ -21,8 +21,11 @@ on:  # yamllint disable-line rule:truthy
         description: Whether to run the Android tests
         value: ${{ jobs.compute-changes.outputs.run-android }}  # bool
       run-ci-fuzz:
-        description: Whether to run the CIFuzz job
+        description: Whether to run the CIFuzz job for 'cpython' fuzzer
         value: ${{ jobs.compute-changes.outputs.run-ci-fuzz }}  # bool
+      run-ci-fuzz-stdlib:
+        description: Whether to run the CIFuzz job for 'python3-libraries' fuzzer
+        value: ${{ jobs.compute-changes.outputs.run-ci-fuzz-stdlib }}  # bool
       run-docs:
         description: Whether to build the docs
         value: ${{ jobs.compute-changes.outputs.run-docs }}  # bool
@@ -56,6 +59,7 @@ jobs:
     outputs:
       run-android: ${{ steps.changes.outputs.run-android }}
       run-ci-fuzz: ${{ steps.changes.outputs.run-ci-fuzz }}
+      run-ci-fuzz-stdlib: ${{ steps.changes.outputs.run-ci-fuzz-stdlib }}
       run-docs: ${{ steps.changes.outputs.run-docs }}
       run-ios: ${{ steps.changes.outputs.run-ios }}
       run-macos: ${{ steps.changes.outputs.run-macos }}

@@ -11,7 +11,7 @@
 
 import os
 import subprocess
-from dataclasses import dataclass
+from dataclasses import dataclass, fields
 from pathlib import Path
 
 TYPE_CHECKING = False
@@ -52,11 +52,59 @@
 MACOS_DIRS = frozenset({"Mac"})
 WASI_DIRS = frozenset({Path("Tools", "wasm")})
 
+LIBRARY_FUZZER_PATHS = frozenset({
+    # All C/CPP fuzzers.
+    Path("configure"),
+    Path(".github/workflows/reusable-cifuzz.yml"),
+    # ast
+    Path("Lib/ast.py"),
+    Path("Python/ast.c"),
+    # configparser
+    Path("Lib/configparser.py"),
+    # csv
+    Path("Lib/csv.py"),
+    Path("Modules/_csv.c"),
+    # decode
+    Path("Lib/encodings/"),
+    Path("Modules/_codecsmodule.c"),
+    Path("Modules/cjkcodecs/"),
+    Path("Modules/unicodedata*"),
+    # difflib
+    Path("Lib/difflib.py"),
+    # email
+    Path("Lib/email/"),
+    # html
+    Path("Lib/html/"),
+    Path("Lib/_markupbase.py"),
+    # http.client
+    Path("Lib/http/client.py"),
+    # json
+    Path("Lib/json/"),
+    Path("Modules/_json.c"),
+    # plist
+    Path("Lib/plistlib.py"),
+    # re
+    Path("Lib/re/"),
+    Path("Modules/_sre/"),
+    # tarfile
+    Path("Lib/tarfile.py"),
+    # tomllib
+    Path("Modules/tomllib/"),
+    # xml
+    Path("Lib/xml/"),
+    Path("Lib/_markupbase.py"),
+    Path("Modules/expat/"),
+    Path("Modules/pyexpat.c"),
+    # zipfile
+    Path("Lib/zipfile/"),
+})
+
 
 @dataclass(kw_only=True, slots=True)
 class Outputs:
     run_android: bool = False
     run_ci_fuzz: bool = False
+    run_ci_fuzz_stdlib: bool = False
     run_docs: bool = False
     run_ios: bool = False
     run_macos: bool = False
@@ -96,6 +144,11 @@ def compute_changes() -> None:
     else:
         print("Branch too old for CIFuzz tests; or no C files were changed")
 
+    if outputs.run_ci_fuzz_stdlib:
+        print("Run CIFuzz tests for libraries")
+    else:
+        print("Branch too old for CIFuzz tests; or no library files were changed")
+
     if outputs.run_docs:
         print("Build documentation")
 
@@ -146,9 +199,18 @@ def get_file_platform(file: Path) -> str | None:
     return None
 
 
+def is_fuzzable_library_file(file: Path) -> bool:
+    return any(
+        (file.is_relative_to(needs_fuzz) and needs_fuzz.is_dir())
+        or (file == needs_fuzz and file.is_file())
+        for needs_fuzz in LIBRARY_FUZZER_PATHS
+    )
+
+
 def process_changed_files(changed_files: Set[Path]) -> Outputs:
     run_tests = False
     run_ci_fuzz = False
+    run_ci_fuzz_stdlib = False
     run_docs = False
     run_windows_tests = False
     run_windows_msi = False
@@ -162,8 +224,8 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
         doc_file = file.suffix in SUFFIXES_DOCUMENTATION or doc_or_misc
 
         if file.parent == GITHUB_WORKFLOWS_PATH:
-            if file.name == "build.yml":
-                run_tests = run_ci_fuzz = True
+            if file.name == "build.yml" or file.name == "reusable-cifuzz.yml":
+                run_tests = run_ci_fuzz = run_ci_fuzz_stdlib = True
                 has_platform_specific_change = False
             if file.name == "reusable-docs.yml":
                 run_docs = True
@@ -194,6 +256,8 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
             ("Modules", "_xxtestfuzz"),
         }:
             run_ci_fuzz = True
+        if not run_ci_fuzz_stdlib and is_fuzzable_library_file(file):
+            run_ci_fuzz_stdlib = True
 
         # Check for changed documentation-related files
         if doc_file:
@@ -227,6 +291,7 @@ def process_changed_files(changed_files: Set[Path]) -> Outputs:
     return Outputs(
         run_android=run_android,
         run_ci_fuzz=run_ci_fuzz,
+        run_ci_fuzz_stdlib=run_ci_fuzz_stdlib,
         run_docs=run_docs,
         run_ios=run_ios,
         run_macos=run_macos,
@@ -261,16 +326,10 @@ def write_github_output(outputs: Outputs) -> None:
         return
 
     with open(os.environ["GITHUB_OUTPUT"], "a", encoding="utf-8") as f:
-        f.write(f"run-android={bool_lower(outputs.run_android)}\n")
-        f.write(f"run-ci-fuzz={bool_lower(outputs.run_ci_fuzz)}\n")
-        f.write(f"run-docs={bool_lower(outputs.run_docs)}\n")
-        f.write(f"run-ios={bool_lower(outputs.run_ios)}\n")
-        f.write(f"run-macos={bool_lower(outputs.run_macos)}\n")
-        f.write(f"run-tests={bool_lower(outputs.run_tests)}\n")
-        f.write(f"run-ubuntu={bool_lower(outputs.run_ubuntu)}\n")
-        f.write(f"run-wasi={bool_lower(outputs.run_wasi)}\n")
-        f.write(f"run-windows-msi={bool_lower(outputs.run_windows_msi)}\n")
-        f.write(f"run-windows-tests={bool_lower(outputs.run_windows_tests)}\n")
+        for field in fields(outputs):
+            name = field.name.replace("_", "-")
+            val = bool_lower(getattr(outputs, field.name))
+            f.write(f"{name}={val}\n")
 
 
 def bool_lower(value: bool, /) -> str: