{"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"}}]}}