GHSA-5vjj-2r48-q622: Pip/zapros vulnerability

Impact

Who is impacted: - Any application using Zapros to make HTTP requests to untrusted servers - Applications that follow redirects to attacker-controlled hosts

Attack vector: - A malicious HTTP server returns a response with many chained content encodings. When the client attempts to decode, it creates a deeply nested decompression chain consuming excessive resources.

Patches

Fixed in version 0.14.0.

The fix adds a hardcoded limit of 5 Content-Encoding layers. Responses exceeding this limit raise DecodingError.

Workarounds

Add middleware that checks for a malicious Content-Encoding header.

python from typing import cast

from zapros import ( AsyncBaseHandler, AsyncBaseMiddleware, BaseHandler, BaseMiddleware, Client, DecodingError, Request, Response, )

MAXDECODELAYERS = 5

class ContentEncodingCheckMiddleware(BaseMiddleware, AsyncBaseMiddleware): def init( self, nexthandler: BaseHandler | AsyncBaseHandler, , maxlayers: int = MAXDECODELAYERS, ) -> None: self.next = cast(BaseHandler, nexthandler) self.asyncnext = cast(AsyncBaseHandler, nexthandler) self.maxlayers = maxlayers

def check(self, response: Response) -> None: encodingheader = response.headers.get("Content-Encoding") if not encodingheader: return

layers = [enc.strip().lower() for enc in encodingheader.split(",") if enc.strip()] if len(layers) > self.maxlayers: raise DecodingError(f"Too many Content-Encoding layers ({len(layers)}), maximum is {self.maxlayers}")

def handle(self, request: Request) -> Response: response = self.next.handle(request) self.check(response) return response

async def ahandle(self, request: Request) -> Response: response = await self.asyncnext.ahandle(request) self.check(response) return response

with Client().wrapwithmiddleware(lambda next: ContentEncodingCheckMiddleware(next)) as client: ...