Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3_CVE-2026-9375

{
    "lastseen": "",
    "description": "urllib3 version 2.6.3 is vulnerable to a decompression bomb bypass in its streaming API (`preload_content=False`) when using Brotli support. The issue arises due to three independent code paths in `response.py` that bypass the `max_length` protection introduced in version 2.6.0 to mitigate CVE-2025-66471. Specifically, negative `max_length` values can be produced due to buffer arithmetic in `read()`, `flush_decoder` unconditionally overrides `max_length` to `-1`, and `_flush_decoder()` passes no limit at all, defaulting to unlimited decompression. This allows a malicious HTTP server to trigger an out-of-memory (OOM) condition by decompressing large payloads into memory, leading to a denial of service (DoS). The vulnerability affects urllib3 2.6.3 and Brotli 1.2.0 and impacts applications and libraries using `requests` or `urllib3` to stream content from untrusted sources.",
    "published": "2026-06-19T18:45:10.409Z",
    "modified": "2026-06-19T18:45:10.409Z",
    "type": "cve",
    "title": "Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3",
    "source": "@huntr_ai",
    "references": "https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23\nhttps://github.com/urllib3/urllib3/commit/2bdcc44d1e163fb5cc48a8662425e35e15adfe6a",
    "id": "CVE-2026-9375",
    "bulletinFamily": "",
    "cwe": [
        "CWE-400"
    ],
    "cvelist": null,
    "sourceData": "urllib3 urllib3/urllib3 unspecified",
    "sourceHref": "",
    "cvss": {
        "score": 7.5,
        "severity": "HIGH",
        "vector": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
        "version": "3.0"
    },
    "cvss2": [],
    "cvss3": {
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        "baseScore": 0,
        "baseSeverity": "",
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        "attackComplexity": "",
        "privilegesRequired": "",
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        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
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            "baseScore": 0,
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "urllib3/urllib3",
    "version": "unspecified",
    "vendor": "urllib3",
    "ai_description": "",
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    "ai_score": 0
}