AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values – header injection / security bypass_CVE-2026-34520

{
    "lastseen": "",
    "description": "AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to version 3.13.4, the C parser (the default for most installs) accepted null bytes and control characters in response headers. This issue has been patched in version 3.13.4.",
    "published": "2026-04-01T20:27:48.350Z",
    "modified": "2026-04-04T03:13:48.418Z",
    "type": "cve",
    "title": "AIOHTTP: C parser (llhttp) accepts null bytes and control characters in response header values - header injection / security bypass",
    "source": "GitHub_M",
    "references": "https://github.com/aio-libs/aiohttp/security/advisories/GHSA-63hf-3vf5-4wqf\nhttps://github.com/aio-libs/aiohttp/commit/9370b9714a7a56003cacd31a9b4ae16eab109ba4\nhttps://github.com/aio-libs/aiohttp/releases/tag/v3.13.4",
    "id": "CVE-2026-34520",
    "bulletinFamily": "",
    "cwe": [
        "CWE-113"
    ],
    "cvelist": null,
    "sourceData": "aio-libs aiohttp < 3.13.4",
    "sourceHref": "",
    "cvss": {
        "score": 2.7,
        "severity": "LOW",
        "vector": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U",
        "version": "4.0"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
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            "privilegesRequired": "",
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            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "aiohttp",
    "version": "< 3.13.4",
    "vendor": "aio-libs",
    "ai_description": "",
    "ai_severity": "",
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    "ai_score": 0
}