{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-45721",
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "state": "PUBLISHED",
        "assignerShortName": "GitHub_M",
        "dateReserved": "2026-05-13T05:51:48.666Z",
        "datePublished": "2026-05-26T16:34:49.985Z",
        "dateUpdated": "2026-05-26T17:15:34.450Z"
    },
    "containers": {
        "cna": {
            "title": "Algernon: handler.lua discovery walks parent directories above the server root",
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-20",
                            "lang": "en",
                            "description": "CWE-20: Improper Input Validation",
                            "type": "CWE"
                        }
                    ]
                },
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-426",
                            "lang": "en",
                            "description": "CWE-426: Untrusted Search Path",
                            "type": "CWE"
                        }
                    ]
                },
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-552",
                            "lang": "en",
                            "description": "CWE-552: Files or Directories Accessible to External Parties",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "metrics": [
                {
                    "cvssV3_1": {
                        "attackComplexity": "HIGH",
                        "attackVector": "NETWORK",
                        "availabilityImpact": "HIGH",
                        "baseScore": 9,
                        "baseSeverity": "CRITICAL",
                        "confidentialityImpact": "HIGH",
                        "integrityImpact": "HIGH",
                        "privilegesRequired": "NONE",
                        "scope": "CHANGED",
                        "userInteraction": "NONE",
                        "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H",
                        "version": "3.1"
                    }
                }
            ],
            "references": [
                {
                    "name": "https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc",
                    "tags": [
                        "x_refsource_CONFIRM"
                    ],
                    "url": "https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc"
                }
            ],
            "affected": [
                {
                    "vendor": "xyproto",
                    "product": "algernon",
                    "versions": [
                        {
                            "version": "< 1.17.7",
                            "status": "affected"
                        }
                    ]
                }
            ],
            "providerMetadata": {
                "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
                "shortName": "GitHub_M",
                "dateUpdated": "2026-05-26T16:34:49.985Z"
            },
            "descriptions": [
                {
                    "lang": "en",
                    "value": "Algernon is a small self-contained pure-Go web server. Prior to 1.17.7, when Algernon is asked for any URL path that resolves to a directory without an index file, DirPage walks upward through parent directories — past the configured server root — looking for a file named handler.lua to execute as the request handler. The loop terminates only after 100 ancestor steps or when filepath.Dir returns ., so on any absolute server-root path the search reaches the filesystem root (/ on Unix, drive letter on Windows). The first handler.lua it finds is loaded into the Lua interpreter with the full Algernon API exposed — including run3(), httpclient, os.execute, io.popen, PQ, MSSQL, raw filesystem access, and the userstate database. Any process that can write handler.lua anywhere in a parent directory of the server root obtains pre-authenticated remote code execution on the next HTTP request. This is reachable without authentication — the lookup happens before the permission check returns a hit (the perm system only gates URL prefixes, not the handler-resolution step), and any URL pointing at a directory without an index triggers the walk. On a fresh stock Algernon install the request GET / is enough. This vulnerability is fixed in 1.17.7."
                }
            ],
            "source": {
                "advisory": "GHSA-xwcr-wm99-g9jc",
                "discovery": "UNKNOWN"
            }
        },
        "adp": [
            {
                "references": [
                    {
                        "url": "https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc",
                        "tags": [
                            "exploit"
                        ]
                    }
                ],
                "metrics": [
                    {
                        "other": {
                            "type": "ssvc",
                            "content": {
                                "timestamp": "2026-05-26T17:13:14.630410Z",
                                "id": "CVE-2026-45721",
                                "options": [
                                    {
                                        "Exploitation": "poc"
                                    },
                                    {
                                        "Automatable": "no"
                                    },
                                    {
                                        "Technical Impact": "total"
                                    }
                                ],
                                "role": "CISA Coordinator",
                                "version": "2.0.3"
                            }
                        }
                    }
                ],
                "title": "CISA ADP Vulnrichment",
                "providerMetadata": {
                    "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
                    "shortName": "CISA-ADP",
                    "dateUpdated": "2026-05-26T17:15:34.450Z"
                }
            }
        ]
    }
}