{"api_version":"1","generated_at":"2026-05-28T01:39:54+00:00","cve":"CVE-2026-45721","urls":{"html":"https://cve.report/CVE-2026-45721","api":"https://cve.report/api/cve/CVE-2026-45721.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-45721","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-45721"},"summary":{"title":"Algernon: handler.lua discovery walks parent directories above the server root","description":"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.","state":"PUBLISHED","assigner":"GitHub_M","published_at":"2026-05-26 17:16:47","updated_at":"2026-05-26 19:26:42"},"problem_types":["CWE-20","CWE-426","CWE-552","CWE-20 CWE-20: Improper Input Validation","CWE-426 CWE-426: Untrusted Search Path","CWE-552 CWE-552: Files or Directories Accessible to External Parties"],"metrics":[{"version":"3.1","source":"security-advisories@github.com","type":"Secondary","score":"9","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","baseScore":9,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"CHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"9","severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","data":{"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":[{"url":"https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc","name":"https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc","refsource":"134c704f-9b21-4f2e-91b3-4a467353bcc0","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-45721","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45721","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"xyproto","product":"algernon","version":"affected < 1.17.7","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"45721","cve":"CVE-2026-45721","epss":"0.002080000","percentile":"0.430880000","score_date":"2026-05-27","updated_at":"2026-05-28 00:02:13"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"adp":[{"metrics":[{"other":{"content":{"id":"CVE-2026-45721","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","timestamp":"2026-05-26T17:13:14.630410Z","version":"2.0.3"},"type":"ssvc"}}],"providerMetadata":{"dateUpdated":"2026-05-26T17:15:34.450Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"references":[{"tags":["exploit"],"url":"https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc"}],"title":"CISA ADP Vulnrichment"}],"cna":{"affected":[{"product":"algernon","vendor":"xyproto","versions":[{"status":"affected","version":"< 1.17.7"}]}],"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."}],"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"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-20","description":"CWE-20: Improper Input Validation","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-426","description":"CWE-426: Untrusted Search Path","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-552","description":"CWE-552: Files or Directories Accessible to External Parties","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-05-26T16:34:49.985Z","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M"},"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"}],"source":{"advisory":"GHSA-xwcr-wm99-g9jc","discovery":"UNKNOWN"},"title":"Algernon: handler.lua discovery walks parent directories above the server root"}},"cveMetadata":{"assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","assignerShortName":"GitHub_M","cveId":"CVE-2026-45721","datePublished":"2026-05-26T16:34:49.985Z","dateReserved":"2026-05-13T05:51:48.666Z","dateUpdated":"2026-05-26T17:15:34.450Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-05-26 17:16:47","lastModifiedDate":"2026-05-26 19:26:42","problem_types":["CWE-20","CWE-426","CWE-552","CWE-20 CWE-20: Improper Input Validation","CWE-426 CWE-426: Untrusted Search Path","CWE-552 CWE-552: Files or Directories Accessible to External Parties"],"metrics":{"cvssMetricV31":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","baseScore":9,"baseSeverity":"CRITICAL","attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"CHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":2.2,"impactScore":6}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"45721","Ordinal":"1","Title":"Algernon: handler.lua discovery walks parent directories above t","CVE":"CVE-2026-45721","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"45721","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Algernon: handler.lua discovery walks parent directories above t"}]}}}