Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`_CVE-2026-52845

{
    "lastseen": "",
    "description": "Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _. This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.",
    "published": "2026-06-23T17:52:01.871Z",
    "modified": "2026-06-23T17:52:01.871Z",
    "type": "cve",
    "title": "Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`",
    "source": "GitHub_M",
    "references": "https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g",
    "id": "CVE-2026-52845",
    "bulletinFamily": "",
    "cwe": [
        "CWE-287",
        "CWE-290",
        "CWE-444"
    ],
    "cvelist": null,
    "sourceData": "caddyserver caddy < 2.11.4",
    "sourceHref": "",
    "cvss": {
        "score": 8.1,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
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            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "caddy",
    "version": "< 2.11.4",
    "vendor": "caddyserver",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}