security: block path traversal, SVG upload, duplicate defs; add tests, docs, license

- Validate paste IDs against ^[a-f0-9]{16}$ before filesystem access
  (blocks read/delete traversal via crafted URLs)
- Remove duplicate ALLOWED_IMAGE_EXTENSIONS that re-allowed SVG
  (XSS via stored SVG); keep magic-byte validation
- Remove duplicate cleanup thread (two background loops were started)
- Unknown expiry keys now default to 1 day instead of never
- request.secure -> request.is_secure (werkzeug 3.x)
- Add gunicorn to requirements (Dockerfile CMD referenced it)
- 11 unit tests, ruff clean, MIT LICENSE, full README (was empty)

.dockerignore

@@ -11,3 +11,4 @@ docker-compose.override.yml
 .dockerignore
 store/
 uploads/
+tests/

LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2025 Jarian Cottingham
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

README.md

@@ -0,0 +1,71 @@
+# paste-bin
+
+A minimal, security-focused paste bin: share text, images, and files with
+expiring links. Built with Flask and file-based storage (no database).
+
+## Features
+
+- Text, image, and file pastes with random 16-hex-char IDs
+- Expiry options: 1 hour, 1 day, 1 week, 1 month, or never
+- Automatic background cleanup of expired pastes
+- Per-IP upload rate limiting (10 uploads / 60 s)
+- Image magic-byte validation; SVG rejected (XSS prevention)
+- Paste-ID format validation (blocks path traversal on read/delete)
+- Security headers: CSP, HSTS, nosniff, frame deny, referrer policy
+- Raw view, pretty view, and download endpoints per paste
+
+## Quick Start
+
+```bash
+pip install -r requirements.txt
+python app.py
+# visit http://localhost:8080
+```
+
+## Configuration
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `PORT` | `8080` | Web server port |
+| `SECRET_KEY` | random | Flask secret key |
+| `UPLOAD_FOLDER` | `./uploads` | Binary file storage |
+| `STORE_FOLDER` | `./store` | Paste metadata + text content |
+
+## Docker
+
+```bash
+docker build -t paste-bin .
+docker run -p 8080:8080 \
+  -v paste-uploads:/app/uploads \
+  -v paste-store:/app/store \
+  paste-bin
+```
+
+Or with compose (mounts persistent volumes):
+
+```bash
+docker compose up -d
+```
+
+## Tests
+
+```bash
+pip install -r requirements.txt pytest
+pytest tests/ -v
+```
+
+Covers paste roundtrips, path-traversal blocking, SVG/magic-byte
+validation, expiry parsing, and rate-limit setup.
+
+## Security Notes
+
+- Uploads are stored under a random ID; extension preserved only for
+  downloads with `Content-Disposition: attachment`.
+- Text pastes are served as `text/plain` (never rendered as HTML).
+- Images are served with `X-Content-Type-Options: nosniff` + restrictive CSP.
+- Paste IDs are validated against `^[a-f0-9]{16}$` before any filesystem
+  access, so crafted URLs cannot read or delete arbitrary files.
+
+## License
+
+MIT — see [LICENSE](LICENSE).

app.py

@@ -1,7 +1,7 @@
 import os
+import re
 import uuid
 import json
-import fcntl
 import secrets
 import time
 import threading
@@ -33,15 +33,13 @@ ALLOWED_IMAGE_MAGIC = {
 }
 ALLOWED_TEXT_EXTENSIONS = {'txt', 'py', 'js', 'ts', 'c', 'cpp', 'h', 'java', 'rb', 'go', 'rs', 'md', 'json', 'xml', 'yaml', 'yml', 'html', 'css', 'sh', 'log', 'csv', 'sql', 'ini', 'cfg', 'toml', 'lua', 'php', 'swift', 'kt', 'scala', 'r', 'pl', 'hs', 'zig', 'nix'}
 
+# Paste IDs are uuid4().hex[:16]; reject anything else to block path traversal.
+PASTE_ID_RE = re.compile(r'^[a-f0-9]{16}$')
+
 _upload_attempts = {}
 _UPLOAD_MAX = 10
 _UPLOAD_WINDOW = 60
 
-_csrf_secret = secrets.token_hex(32)
-
-ALLOWED_IMAGE_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif', 'bmp', 'webp', 'svg', 'tiff'}
-ALLOWED_TEXT_EXTENSIONS = {'txt', 'py', 'js', 'ts', 'c', 'cpp', 'h', 'java', 'rb', 'go', 'rs', 'md', 'json', 'xml', 'yaml', 'yml', 'html', 'css', 'sh', 'log', 'csv', 'sql', 'ini', 'cfg', 'toml', 'lua', 'php', 'swift', 'kt', 'scala', 'r', 'pl', 'hs', 'zig', 'nix'}
-
 
 def ensure_dirs():
     os.makedirs(app.config['UPLOAD_FOLDER'], exist_ok=True)
@@ -53,18 +51,17 @@ def generate_id():
 
 
 def parse_expiry(expiry_key):
+    """Map an expiry option to an ISO timestamp; unknown keys default to 1 day."""
     if expiry_key == 'forever':
         return None
     now = datetime.now(timezone.utc)
     if expiry_key == '1h':
         return (now + timedelta(hours=1)).isoformat()
-    elif expiry_key == '1d':
-        return (now + timedelta(days=1)).isoformat()
     elif expiry_key == '1w':
         return (now + timedelta(weeks=1)).isoformat()
     elif expiry_key == '1m':
         return (now + timedelta(days=30)).isoformat()
-    return None
+    return (now + timedelta(days=1)).isoformat()
 
 
 def store_paste(paste_id, paste_data):
@@ -77,6 +74,8 @@ def store_paste(paste_id, paste_data):
 
 
 def load_paste(paste_id):
+    if not PASTE_ID_RE.match(paste_id):
+        return None
     store_path = os.path.join(app.config['STORE_FOLDER'], paste_id)
     if not os.path.exists(store_path):
         return None
@@ -161,17 +160,6 @@ def save_text_content(paste_id, content):
 # Fix #16 - ensure_dirs at startup only, not every request
 ensure_dirs()
 
-# Fix #1 - scheduled cleanup of expired pastes
-def _cleanup_loop():
-    while True:
-        time.sleep(300)
-        try:
-            cleanup_expired()
-        except Exception as e:
-            print(f"Cleanup error: {e}")
-
-threading.Thread(target=_cleanup_loop, daemon=True).start()
-
 
 @app.after_request
 def add_security_headers(response):
@@ -180,7 +168,7 @@ def add_security_headers(response):
     response.headers['X-XSS-Protection'] = '1; mode=block'
     response.headers['Referrer-Policy'] = 'strict-origin-when-cross-origin'
     response.headers['Content-Security-Policy'] = "default-src 'self'; img-src 'self' data:; style-src 'self' 'unsafe-inline'"
-    if request.secure:
+    if request.is_secure:
         response.headers['Strict-Transport-Security'] = 'max-age=31536000; includeSubDomains'
     return response
 

pyproject.toml

@@ -0,0 +1,42 @@
+[project]
+name = "paste-bin"
+version = "1.0.0"
+description = "Minimal security-focused paste bin: text, image, and file sharing with expiring links"
+readme = "README.md"
+requires-python = ">=3.9"
+license = { text = "MIT" }
+authors = [{ name = "Jarian Cottingham", email = "jarianc@proton.me" }]
+keywords = ["paste", "paste-bin", "sharing", "flask"]
+classifiers = [
+    "License :: OSI Approved :: MIT License",
+    "Programming Language :: Python :: 3",
+]
+dependencies = [
+    "flask>=3.0,<4.0",
+    "werkzeug>=3.0,<4.0",
+]
+
+[project.optional-dependencies]
+dev = [
+    "pytest>=7.0",
+    "ruff>=0.1.0",
+]
+
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
+[tool.setuptools]
+py-modules = ["app"]
+
+[tool.ruff]
+line-length = 120
+target-version = "py39"
+exclude = [".git", "uploads", "store"]
+
+[tool.ruff.lint]
+select = ["E", "F", "W"]
+ignore = ["E501"]
+
+[tool.pytest.ini_options]
+testpaths = ["tests"]

tests/test_app.py

@@ -0,0 +1,119 @@
+"""Unit tests for paste-bin."""
+
+import io
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+import app as app_module  # noqa: E402
+
+
+@pytest.fixture()
+def client(tmp_path, monkeypatch):
+    app_module.app.config['TESTING'] = True
+    app_module.app.config['UPLOAD_FOLDER'] = str(tmp_path / 'uploads')
+    app_module.app.config['STORE_FOLDER'] = str(tmp_path / 'store')
+    app_module.ensure_dirs()
+    with app_module.app.test_client() as c:
+        yield c
+
+
+def test_index_returns_200(client):
+    resp = client.get('/')
+    assert resp.status_code == 200
+
+
+def test_text_paste_roundtrip(client):
+    resp = client.post('/paste', data={'paste_type': 'text', 'content': 'hello world', 'expiry': '1d'})
+    assert resp.status_code == 302
+    paste_id = resp.headers['Location'].rsplit('/', 1)[-1]
+    assert len(paste_id) == 16
+
+    view = client.get(f'/{paste_id}')
+    assert view.status_code == 200
+    assert b'hello world' in view.data
+
+    raw = client.get(f'/{paste_id}/raw')
+    assert raw.status_code == 200
+    assert raw.data == b'hello world'
+
+    dl = client.get(f'/{paste_id}/download')
+    assert dl.status_code == 200
+    assert dl.data == b'hello world'
+
+
+def test_empty_content_rejected(client):
+    resp = client.post('/paste', data={'paste_type': 'text', 'content': '   ', 'expiry': '1d'})
+    assert resp.status_code == 400
+
+
+def test_invalid_paste_type_rejected(client):
+    resp = client.post('/paste', data={'paste_type': 'bogus', 'content': 'x'})
+    assert resp.status_code == 400
+
+
+def test_unknown_paste_404(client):
+    assert client.get('/' + 'a' * 16).status_code == 404
+
+
+def test_path_traversal_paste_id_blocked(client, tmp_path):
+    outside = tmp_path / 'secret.txt'
+    outside.write_text('top secret')
+    for evil in ['..%2F..%2Fsecret.txt', '....//secret.txt', 'a' * 14 + '/../../secret.txt']:
+        resp = client.get('/' + evil)
+        assert resp.status_code == 404
+    assert outside.exists()
+
+
+def test_svg_upload_rejected(client):
+    png_bytes = b'<svg xmlns="http://www.w3.org/2000/svg"><script>alert(1)</script></svg>'
+    resp = client.post(
+        '/paste',
+        data={'paste_type': 'image', 'file': (io.BytesIO(png_bytes), 'x.svg', 'image/svg+xml')},
+        content_type='multipart/form-data',
+    )
+    assert resp.status_code == 400
+
+
+def test_png_magic_validation(client):
+    fake = b'not-a-real-png'
+    resp = client.post(
+        '/paste',
+        data={'paste_type': 'image', 'file': (io.BytesIO(fake), 'x.png', 'image/png')},
+        content_type='multipart/form-data',
+    )
+    assert resp.status_code == 400
+
+
+def test_valid_png_upload(client):
+    png = b'\x89PNG\r\n\x1a\n' + b'\x00' * 32
+    resp = client.post(
+        '/paste',
+        data={'paste_type': 'image', 'file': (io.BytesIO(png), 'pic.png', 'image/png')},
+        content_type='multipart/form-data',
+    )
+    assert resp.status_code == 302
+    paste_id = resp.headers['Location'].rsplit('/', 1)[-1]
+    assert client.get(f'/{paste_id}').status_code == 200
+
+
+def test_expiry_parsing():
+    assert app_module.parse_expiry('forever') is None
+    for key in ['1h', '1d', '1w', '1m', 'bogus-key']:
+        result = app_module.parse_expiry(key)
+        assert result is not None
+        from datetime import datetime
+
+        datetime.fromisoformat(result)
+
+
+def test_store_and_load_paste(tmp_path, monkeypatch):
+    app_module.app.config['STORE_FOLDER'] = str(tmp_path / 'store')
+    app_module.ensure_dirs()
+    app_module.store_paste('ab' * 8, {'type': 'text', 'title': 't'})
+    paste = app_module.load_paste('ab' * 8)
+    assert paste['title'] == 't'
+    assert app_module.load_paste('../etc/passwd') is None