{"id":"CVE-2026-48126","state":"PUBLISHED","title":"Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir","description":"Algernon is a small self-contained pure-Go web server. Prior to 1.17.8, when algernon is started with --domain (or --letsencrypt, which silently turns on --domain at engine/flags.go:372), the request handler resolves the served directory by joining the configured --dir with the value of the client-supplied Host header. The join is performed by filepath.Join with no validation, so a Host: .. header walks one level above the document root. Subsequent file resolution then exposes everything in that parent directory — arbitrary file read, full directory listing, and, if any .lua file is present, server-side Lua execution. This vulnerability is fixed in 1.17.8.","publishedAt":"2026-05-26T16:44:09.104Z","updatedAt":"2026-05-26T17:27:56.507Z","severity":{"score":8.2,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["xyproto algernon"],"affected":[{"vendor":"xyproto","product":"algernon","versions":[{"version":"< 1.17.8","status":"affected"}]}],"references":["https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv"],"weaknesses":["CWE-22","CWE-23","CWE-644"],"ingestedAt":"2026-10-29T20:12:07.131Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/48xxx/CVE-2026-48126.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-48126","state":"PUBLISHED","datePublished":"2026-05-26T16:44:09.104Z","dateUpdated":"2026-05-26T17:27:56.507Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-05-20T18:46:58.291Z"},"containers":{"cna":{"title":"Algernon: Host header path traversal in --domain mode reads files and runs Lua from parent dir","descriptions":[{"lang":"en","value":"Algernon is a small self-contained pure-Go web server. Prior to 1.17.8, when algernon is started with --domain (or --letsencrypt, which silently turns on --domain at engine/flags.go:372), the request handler resolves the served directory by joining the configured --dir with the value of the client-supplied Host header. The join is performed by filepath.Join with no validation, so a Host: .. header walks one level above the document root. Subsequent file resolution then exposes everything in that parent directory — arbitrary file read, full directory listing, and, if any .lua file is present, server-side Lua execution. This vulnerability is fixed in 1.17.8."}],"affected":[{"vendor":"xyproto","product":"algernon","versions":[{"version":"< 1.17.8","status":"affected"}]}],"references":[{"url":"https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv","name":"https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv","tags":["x_refsource_CONFIRM"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.2,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"LOW","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-22","lang":"en","description":"CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-23","lang":"en","description":"CWE-23: Relative Path Traversal","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-644","lang":"en","description":"CWE-644: Improper Neutralization of HTTP Headers for Scripting Syntax","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-05-26T16:44:09.104Z"},"source":{"advisory":"GHSA-jc3j-x6pg-4hmv","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/xyproto/algernon/security/advisories/GHSA-jc3j-x6pg-4hmv","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-05-26T17:27:29.590530Z","id":"CVE-2026-48126","options":[{"Exploitation":"poc"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-05-26T17:27:56.507Z"}}]}}}