{"id":"CVE-2026-61541","aliases":["GHSA-5vjj-2r48-q622","PYSEC-2026-4181"],"url":"https://o3.security/vulnerability/CVE-2026-61541","summary":"Zapros has an Unbounded Content-Encoding decompression chain that allows denial of service","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    ) -> 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) -> 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) > 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) -> Response:\n        response = self.next.handle(request)\n        self._check(response)\n        return response\n\n    async def ahandle(self, request: Request) -> 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```","published":"2026-09-21T21:21:21.321Z","modified":"2026-10-21T02:58:52.143113568Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"zapros","fixedVersion":"0.14.0"}],"fix":{"url":"https://github.com/kap-sh/zapros/commit/7971fbca9707eb01455ca2d73416ac091f96908b","label":"kap-sh/zapros@7971fbc"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61541.json"},{"type":"ADVISORY","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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:58:52.143113568Z"}}