GHSA-5VJJ-2R48-Q622

Vulnerability from github – Published: 2026-09-23 13:58 – Updated: 2026-09-23 13:58
VLAI
Summary
Zapros has an Unbounded Content-Encoding decompression chain that allows denial of service
Details

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.

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:
    ...
Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "zapros"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.14.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-61541"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-23T13:58:35Z",
    "nvd_published_at": "2026-09-21T22:16:57Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\n**Who is impacted**:\n  - Any application using Zapros to make HTTP requests to untrusted servers\n  - Applications that follow redirects to attacker-controlled hosts\n\n**Attack vector**:\n  - 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.\n\n### Patches\n\nFixed in version 0.14.0.\n\n  The fix adds a hardcoded limit of **5** `Content-Encoding` layers. Responses exceeding this limit raise `DecodingError`.\n\n### Workarounds\n\nAdd middleware that checks for a malicious Content-Encoding header.\n\n```python\nfrom typing import cast\n\nfrom zapros import (\n    AsyncBaseHandler,\n    AsyncBaseMiddleware,\n    BaseHandler,\n    BaseMiddleware,\n    Client,\n    DecodingError,\n    Request,\n    Response,\n)\n\nMAX_DECODE_LAYERS = 5\n\n\nclass ContentEncodingCheckMiddleware(BaseMiddleware, AsyncBaseMiddleware):\n    def __init__(\n        self,\n        next_handler: BaseHandler | AsyncBaseHandler,\n        *,\n        max_layers: int = MAX_DECODE_LAYERS,\n    ) -\u003e None:\n        self.next = cast(BaseHandler, next_handler)\n        self.async_next = cast(AsyncBaseHandler, next_handler)\n        self._max_layers = max_layers\n\n    def _check(self, response: Response) -\u003e None:\n        encoding_header = response.headers.get(\"Content-Encoding\")\n        if not encoding_header:\n            return\n\n        layers = [enc.strip().lower() for enc in encoding_header.split(\",\") if enc.strip()]\n        if len(layers) \u003e self._max_layers:\n            raise DecodingError(f\"Too many Content-Encoding layers ({len(layers)}), maximum is {self._max_layers}\")\n\n    def handle(self, request: Request) -\u003e Response:\n        response = self.next.handle(request)\n        self._check(response)\n        return response\n\n    async def ahandle(self, request: Request) -\u003e Response:\n        response = await self.async_next.ahandle(request)\n        self._check(response)\n        return response\n\n\nwith Client().wrap_with_middleware(lambda next: ContentEncodingCheckMiddleware(next)) as client:\n    ...\n```",
  "id": "GHSA-5vjj-2r48-q622",
  "modified": "2026-09-23T13:58:35Z",
  "published": "2026-09-23T13:58:35Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/kap-sh/zapros/security/advisories/GHSA-5vjj-2r48-q622"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-61541"
    },
    {
      "type": "WEB",
      "url": "https://github.com/kap-sh/zapros/commit/7971fbca9707eb01455ca2d73416ac091f96908b"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/kap-sh/zapros"
    },
    {
      "type": "WEB",
      "url": "https://github.com/kap-sh/zapros/releases/tag/v0.14.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Zapros has an Unbounded Content-Encoding decompression chain that allows denial of service"
}



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