Sign media URLs to avoid becoming an open proxy

Signatures are valid for ~1 week.
main
Kevin Wallace 2022-11-04 01:59:40 -07:00 committed by Thomas Sileo
parent 540b9d1470
commit a4cfd65009
4 changed files with 41 additions and 9 deletions

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@ -1,4 +1,5 @@
import hashlib import hashlib
import hmac
import os import os
import secrets import secrets
from pathlib import Path from pathlib import Path
@ -250,3 +251,7 @@ def verify_csrf_token(
detail=f"The security token has expired, {please_try_again}", detail=f"The security token has expired, {please_try_again}",
) )
return None return None
def hmac_sha256():
return hmac.new(CONFIG.secret.encode(), digestmod=hashlib.sha256)

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@ -48,6 +48,7 @@ from app import boxes
from app import config from app import config
from app import httpsig from app import httpsig
from app import indieauth from app import indieauth
from app import media
from app import micropub from app import micropub
from app import models from app import models
from app import templates from app import templates
@ -1128,14 +1129,17 @@ def _add_cache_control(headers: dict[str, str]) -> dict[str, str]:
return {**headers, "Cache-Control": "max-age=31536000"} return {**headers, "Cache-Control": "max-age=31536000"}
@app.get("/proxy/media/{encoded_url}") @app.get("/proxy/media/{exp}/{sig}/{encoded_url}")
async def serve_proxy_media( async def serve_proxy_media(
request: Request, request: Request,
exp: int,
sig: str,
encoded_url: str, encoded_url: str,
) -> StreamingResponse | PlainTextResponse: ) -> StreamingResponse | PlainTextResponse:
# Decode the base64-encoded URL # Decode the base64-encoded URL
url = base64.urlsafe_b64decode(encoded_url).decode() url = base64.urlsafe_b64decode(encoded_url).decode()
check_url(url) check_url(url)
media.verify_proxied_media_sig(exp, url, sig)
proxy_resp = await _proxy_get(request, url, stream=True) proxy_resp = await _proxy_get(request, url, stream=True)
@ -1168,9 +1172,11 @@ async def serve_proxy_media(
) )
@app.get("/proxy/media/{encoded_url}/{size}") @app.get("/proxy/media/{exp}/{sig}/{encoded_url}/{size}")
async def serve_proxy_media_resized( async def serve_proxy_media_resized(
request: Request, request: Request,
exp: int,
sig: str,
encoded_url: str, encoded_url: str,
size: int, size: int,
) -> PlainTextResponse: ) -> PlainTextResponse:
@ -1180,6 +1186,7 @@ async def serve_proxy_media_resized(
# Decode the base64-encoded URL # Decode the base64-encoded URL
url = base64.urlsafe_b64decode(encoded_url).decode() url = base64.urlsafe_b64decode(encoded_url).decode()
check_url(url) check_url(url)
media.verify_proxied_media_sig(exp, url, sig)
if cached_resp := _RESIZED_CACHE.get((url, size)): if cached_resp := _RESIZED_CACHE.get((url, size)):
resized_content, resized_mimetype, resp_headers = cached_resp resized_content, resized_mimetype, resp_headers = cached_resp

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@ -1,15 +1,40 @@
import base64 import base64
import time
from app.config import BASE_URL from app.config import BASE_URL
from app.config import hmac_sha256
SUPPORTED_RESIZE = [50, 740] SUPPORTED_RESIZE = [50, 740]
EXPIRY_PERIOD = 86400
EXPIRY_LENGTH = 7
class InvalidProxySignatureError(Exception):
pass
def proxied_media_sig(expires: int, url: str) -> str:
hm = hmac_sha256()
hm.update(f'{expires}'.encode())
hm.update(b'|')
hm.update(url.encode())
return base64.urlsafe_b64encode(hm.digest()).decode()
def verify_proxied_media_sig(expires: int, url: str, sig: str) -> None:
now = int(time.time() / EXPIRY_PERIOD)
expected = proxied_media_sig(expires, url)
if now > expires or sig != expected:
raise InvalidProxySignatureError("invalid or expired media")
def proxied_media_url(url: str) -> str: def proxied_media_url(url: str) -> str:
if url.startswith(BASE_URL): if url.startswith(BASE_URL):
return url return url
expires = int(time.time() / EXPIRY_PERIOD) + EXPIRY_LENGTH
sig = proxied_media_sig(expires, url)
return BASE_URL + "/proxy/media/" + base64.urlsafe_b64encode(url.encode()).decode() return BASE_URL + f"/proxy/media/{expires}/{sig}/" + base64.urlsafe_b64encode(url.encode()).decode()
def resized_media_url(url: str, size: int) -> str: def resized_media_url(url: str, size: int) -> str:

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@ -60,12 +60,7 @@ def _filter_domain(text: str) -> str:
def _media_proxy_url(url: str | None) -> str: def _media_proxy_url(url: str | None) -> str:
if not url: if not url:
return BASE_URL + "/static/nopic.png" return BASE_URL + "/static/nopic.png"
return proxied_media_url(url)
if url.startswith(BASE_URL):
return url
encoded_url = base64.urlsafe_b64encode(url.encode()).decode()
return BASE_URL + f"/proxy/media/{encoded_url}"
def is_current_user_admin(request: Request) -> bool: def is_current_user_admin(request: Request) -> bool: