snapshot: preserve upload hardening phase

backend/workflows/upload_validation.py

@@ -0,0 +1,147 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from django import forms
+from django.utils.translation import gettext as _
+
+
+def _header_matches(extension: str, header: bytes) -> bool:
+    extension = extension.lower().lstrip(".")
+    if extension == "png":
+        return header.startswith(b"\x89PNG\r\n\x1a\n")
+    if extension in {"jpg", "jpeg"}:
+        return header.startswith(b"\xff\xd8\xff")
+    if extension == "webp":
+        return header.startswith(b"RIFF") and header[8:12] == b"WEBP"
+    if extension == "pdf":
+        return header.startswith(b"%PDF")
+    if extension == "ico":
+        return header.startswith(b"\x00\x00\x01\x00")
+    if extension == "svg":
+        text = header.decode("utf-8", errors="ignore").lower()
+        return "<svg" in text
+    return False
+
+
+def validate_uploaded_file(
+    uploaded_file,
+    *,
+    allowed_extensions: set[str],
+    max_size_bytes: int,
+    allowed_content_types: set[str] | None = None,
+    invalid_type_message: str,
+    size_message: str,
+    unreadable_message: str,
+) -> None:
+    if not uploaded_file:
+        return
+
+    if getattr(uploaded_file, "size", 0) > max_size_bytes:
+        raise forms.ValidationError(size_message)
+
+    extension = Path(getattr(uploaded_file, "name", "")).suffix.lower().lstrip(".")
+    if extension not in allowed_extensions:
+        raise forms.ValidationError(invalid_type_message)
+
+    content_type = (getattr(uploaded_file, "content_type", "") or "").lower().strip()
+    if allowed_content_types and content_type and content_type not in allowed_content_types:
+        raise forms.ValidationError(invalid_type_message)
+
+    try:
+        header = uploaded_file.read(512)
+        uploaded_file.seek(0)
+    except Exception as exc:
+        raise forms.ValidationError(unreadable_message) from exc
+
+    if not _header_matches(extension, header):
+        raise forms.ValidationError(invalid_type_message)
+
+
+def validate_avatar_upload(uploaded_file) -> None:
+    validate_uploaded_file(
+        uploaded_file,
+        allowed_extensions={"png", "jpg", "jpeg", "webp", "svg"},
+        max_size_bytes=5 * 1024 * 1024,
+        allowed_content_types={
+            "image/png",
+            "image/x-png",
+            "image/jpeg",
+            "image/jpg",
+            "image/pjpeg",
+            "image/webp",
+            "image/svg+xml",
+        },
+        invalid_type_message=_("Bitte ein PNG-, JPG-, WEBP- oder SVG-Bild hochladen."),
+        size_message=_("Das Profilbild darf maximal 5 MB groß sein."),
+        unreadable_message=_("Die Bilddatei konnte nicht gelesen werden."),
+    )
+
+
+def validate_logo_upload(uploaded_file) -> None:
+    validate_uploaded_file(
+        uploaded_file,
+        allowed_extensions={"svg", "png", "jpg", "jpeg", "webp"},
+        max_size_bytes=5 * 1024 * 1024,
+        allowed_content_types={
+            "image/png",
+            "image/x-png",
+            "image/jpeg",
+            "image/jpg",
+            "image/pjpeg",
+            "image/webp",
+            "image/svg+xml",
+        },
+        invalid_type_message=_("Bitte ein SVG-, PNG-, JPG- oder WEBP-Bild hochladen."),
+        size_message=_("Das Logo darf maximal 5 MB groß sein."),
+        unreadable_message=_("Die Logo-Datei konnte nicht gelesen werden."),
+    )
+
+
+def validate_favicon_upload(uploaded_file) -> None:
+    validate_uploaded_file(
+        uploaded_file,
+        allowed_extensions={"ico", "png", "svg", "webp"},
+        max_size_bytes=2 * 1024 * 1024,
+        allowed_content_types={
+            "image/x-icon",
+            "image/vnd.microsoft.icon",
+            "image/png",
+            "image/x-png",
+            "image/webp",
+            "image/svg+xml",
+        },
+        invalid_type_message=_("Bitte eine ICO-, PNG-, SVG- oder WEBP-Datei hochladen."),
+        size_message=_("Das Favicon darf maximal 2 MB groß sein."),
+        unreadable_message=_("Die Favicon-Datei konnte nicht gelesen werden."),
+    )
+
+
+def validate_pdf_upload(uploaded_file) -> None:
+    validate_uploaded_file(
+        uploaded_file,
+        allowed_extensions={"pdf"},
+        max_size_bytes=10 * 1024 * 1024,
+        allowed_content_types={"application/pdf"},
+        invalid_type_message=_("Bitte eine gültige PDF-Datei hochladen."),
+        size_message=_("Der PDF-Briefkopf darf maximal 10 MB groß sein."),
+        unreadable_message=_("Die PDF-Datei konnte nicht gelesen werden."),
+    )
+
+
+def validate_signature_upload(uploaded_file) -> None:
+    validate_uploaded_file(
+        uploaded_file,
+        allowed_extensions={"png", "jpg", "jpeg"},
+        max_size_bytes=4 * 1024 * 1024,
+        allowed_content_types={
+            "image/png",
+            "image/x-png",
+            "image/jpeg",
+            "image/jpg",
+            "image/pjpeg",
+        },
+        invalid_type_message=_("Bitte eine PNG- oder JPG-Datei hochladen."),
+        size_message=_("Die Signatur-Datei ist zu groß (max. 4 MB)."),
+        unreadable_message=_("Die Signatur-Datei konnte nicht gelesen werden."),
+    )