{"cve":"CVE-2026-45721","nvd":{"published":"2026-05-26T17:16:47.750","modified":"2026-07-24T11:10:00.170","status":"Deferred","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H","score":9.0},"cwes":["CWE-20","CWE-426","CWE-552"],"references":["https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc","https://github.com/xyproto/algernon/security/advisories/GHSA-xwcr-wm99-g9jc"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:36:28.938604137+00:00"},"epss":{"cve":"CVE-2026-45721","score":0.00437,"percentile":0.37977,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-xwcr-wm99-g9jc","url":"https://osv.dev/vulnerability/GHSA-xwcr-wm99-g9jc","summary":"Algernon: handler.lua discovery walks parent directories above the server root","modified":"2026-06-25T23:11:38.757764688Z","packages":[{"ecosystem":"Go","name":"github.com/xyproto/algernon","purl":"pkg:golang/github.com/xyproto/algernon","ranges":["<1.17.7"],"fixed":["1.17.7"]}]},{"id":"GO-2026-5772","url":"https://osv.dev/vulnerability/GO-2026-5772","summary":"Algernon: handler.lua discovery walks parent directories above the server root in github.com/xyproto/algernon","modified":"2026-06-25T23:01:17.138102245Z","packages":[{"ecosystem":"Go","name":"github.com/xyproto/algernon","purl":"pkg:golang/github.com/xyproto/algernon","ranges":["<1.17.7"],"fixed":["1.17.7"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}