Security readout for executives and security teams
Plain-English summary
Applications using the Node.js basic-ftp library before 5.2.0 may write downloaded files outside the intended folder when connected to a malicious FTP server. This can overwrite application or system files, creating integrity and availability risk. The vendor advisory states version 5.2.0 patches the issue.
Executive priority
Treat as urgent for applications that download from FTP servers outside your direct control. The vulnerability can allow file overwrite through normal client behavior, and a patched version is available. Prioritize dependency updates in affected Node.js applications and validate where downloadToDir() is used.
Technical view
CVE-2026-27699 is a CWE-22 path traversal flaw in basic-ftp downloadToDir(). A malicious FTP server can return directory entries containing traversal sequences, causing client-side writes outside the chosen destination directory. Affected versions are before 5.2.0. CVSS is 9.1: network attack vector, low complexity, no privileges or user interaction required.
Likely exposure
Exposure is most likely in Node.js services, scripts, or automation that use basic-ftp downloadToDir() against FTP servers, especially untrusted or partner-managed servers. Systems that do not use basic-ftp, use version 5.2.0 or later, or do not call downloadToDir() are less likely exposed.
Exploitation context
The provided sources do not state active exploitation, and the CVE is not marked KEV. Exploitation requires the client application to connect to a malicious or compromised FTP server that can control directory listing filenames. Impact is file write outside the intended download directory, with high integrity and availability consequences.
Researcher notes
The key exposure condition is malicious server-controlled directory listings reaching downloadToDir(). Sources identify the vulnerable package and patched version, but do not provide evidence of exploitation in the wild. Avoid assuming broader FTP client impact beyond basic-ftp versions before 5.2.0.
Mitigation direction
- Upgrade basic-ftp to version 5.2.0 or later.
- Prioritize systems downloading from untrusted, external, or partner FTP servers.
- Review vendor advisory and release notes for implementation-specific guidance.
- Restrict FTP server trust where immediate upgrade is not possible.
Validation and detection
- Check package manifests and lockfiles for basic-ftp versions below 5.2.0.
- Identify code paths using downloadToDir().
- Inventory applications connecting to externally controlled FTP servers.
- Confirm deployed builds include basic-ftp 5.2.0 or later.
- Review logs for unexpected file writes outside download directories.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-22: File access and web shell behavior lookup
File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupFile access behavior lookup
The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-27699 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.1 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H3.95.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.1CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/patrickjuchli/basic-ftp/security/advisories/GHSA-5rq4-664w-9x2cCVE reference · x_refsource_CONFIRM
- https://github.com/patrickjuchli/basic-ftp/commit/2a2a0e6514357b9eda07c2f8afbd3f04727a7cd9CVE reference · x_refsource_MISC
- https://github.com/patrickjuchli/basic-ftp/releases/tag/v5.2.0CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.