CVE-2026-61541

Zapros has an Unbounded Content-Encoding decompression chain that allows denial of service

from typing import cast

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

MAX_DECODE_LAYERS = 5


class ContentEncodingCheckMiddleware(BaseMiddleware, AsyncBaseMiddleware):
    def __init__(
        self,
        next_handler: BaseHandler | AsyncBaseHandler,
        *,
        max_layers: int = MAX_DECODE_LAYERS,
    ) -> None:
        self.next = cast(BaseHandler, next_handler)
        self.async_next = cast(AsyncBaseHandler, next_handler)
        self._max_layers = max_layers

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

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

    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.async_next.ahandle(request)
        self._check(response)
        return response


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

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.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

Kodem intelligence

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Fixed in version 0.14.0.

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

1. What is CVE-2026-61541? CVE-2026-61541 is a medium-severity allocation of resources without limits or throttling vulnerability in zapros (pip), affecting versions < 0.14.0. It is fixed in 0.14.0. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. Which versions of zapros are affected by CVE-2026-61541? zapros (pip) versions < 0.14.0 is affected.
3. Is there a fix for CVE-2026-61541? Yes. CVE-2026-61541 is fixed in 0.14.0. Upgrade to this version or later.
4. Is CVE-2026-61541 exploitable, and should I be worried? Whether CVE-2026-61541 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-61541 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-61541? Upgrade zapros to 0.14.0 or later.

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