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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

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 · score source

EPSS

• CVE-2026-102990: 0.37% estimated exploitation activity in the next 30 days; percentile 30.98 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Client.list() parses the server's directory listing with the Unix-style parser in parseListUnix.js. Its RELINE 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: Prints list() blocked 39.75s; heartbeats fired: 0, versus ~0.06s for a normal…

Published by the source

1 Oct 2026, 14:42 UTC

Last modified by the source

1 Oct 2026, 15:00 UTC

Source last checked

26 Oct 2026, 13:06 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c475-qrg2-pj4r

2. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-c475-qrg2-pj4r

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-c475-qrg2-pj4r

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# Patch Next advisory brief: CVE-2026-102990

Advisory: basic-ftp: Quadratic-time CPU denial of service in Client.list() Unix directory-listing parser (RE_LINE backtracking)
IDs: CVE-2026-102990, GHSA-c475-qrg2-pj4r
Record: https://patchnext.com/advisories/cve-2026-102990 (revision 4, source checked 26 Oct 2026, 13:06 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: basic-ftp 6.2.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm basic-ftp: affected <= 6.2.0; fixed in 6.2.1

## Suggested inspection (read-only)
- `npm ls basic-ftp --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on basic-ftp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c475-qrg2-pj4r (GitHub-reviewed advisory GHSA-c475-qrg2-pj4r lists affected ranges: npm basic-ftp >=0 <=6.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-c475-qrg2-pj4r (OSV record GHSA-c475-qrg2-pj4r lists affected ranges: npm basic-ftp >=0 <6.2.1 (fixed))

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