Wing FTP Server Improper Neutralization of Null Byte or NUL Character Vulnerability (CVE-2025-47812)

What is affected, what to do

In Wing FTP Server before 7.4.4. the user and admin web interfaces mishandle '\0' bytes, ultimately allowing injection of arbitrary Lua code into user session files. This can be used to execute arbitrary system commands with the privileges of the FTP service (root or SYSTEM by default).

The vulnerability is being actively exploited; treat it as a priority. Update Wftpserver Wing FTP Server to version 7.4.4. Immediate actions, mitigation and detection rules are in the runbook below.

Affected

• Wftpserver Wing FTP Server lt *..7.4.4

Fixed in

• Wftpserver Wing FTP Server 7.4.4

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Metrics

Response and mitigation

1. 01

   Runbook step 1

   Immediate response (0-24 h)

   • Upgrade Wing FTP Server to 7.4.4 or later immediately — this is the only complete fix for the NUL-byte injection in both the user and admin web interfaces.
   • Disable anonymous FTP accounts right away (admin console → Domain Settings → Anonymous Login = Off); the flaw is explicitly exploitable without valid credentials.
   • Remove web interfaces (default TCP/5466 HTTP, TCP/5467 HTTPS for the user UI, TCP/5466 for admin) from the public internet — restrict access to VPN or a management VLAN until patched.
   • Reconfigure the FTP service to run under a dedicated unprivileged account instead of root/SYSTEM to reduce blast radius during post-exploitation.
   • Forensically review the session directory (C:\Program Files (x86)\Wing FTP Server\Session\ or /usr/local/wftpserver/session/) for unexpected .lua files, modified session files, and child processes of the FTP service dating back to June 2025 — a public PoC exists and exploitation has been observed since July 2025.
   • Rotate all local FTP user passwords and admin credentials; where compromise is suspected, rebuild the host from scratch, as RCE as root/SYSTEM equals full takeover.
2. 02

   Runbook step 2

   Mitigation layers

   • Network segmentation: move Wing FTP into an isolated DMZ zone, enforce egress filtering (no outbound traffic to the internet except explicitly required destinations), restrict admin UI access to a dedicated admin jump-host subnet.
   • Deploy a WAF or reverse proxy in front of the web UI and block requests containing %00, \x00 or raw null bytes in URL, parameters (notably the username field on /loginok.html) and POST bodies.
   • IPS signature: HTTP POST to /loginok.html or /login.html containing a URL-encoded NUL byte (%00) in the username field — fire high-severity alert and drop.
   • Filesystem hardening: mount the session directory noexec (Linux) or restrict ACLs so the FTP service account cannot load Lua modules; constrain the daemon with AppArmor or SELinux.
   • EDR rule: process creation of cmd.exe, powershell.exe, /bin/sh, /bin/bash with parent wftpserver.exe or wftpd as critical alert — the FTP service does not spawn shells under normal operation.
   • Protect the admin interface with an IP allowlist, MFA (where supported), and a non-default port; verify default admin credentials have been changed.
3. 03

   Runbook step 3

   Detection rules

   • Web access logs: pattern POST /loginok.html with %00, \x00 or \0 in the username parameter — Sigma shape: selection: cs-uri-query|contains: '%00' AND cs-uri-stem|endswith: 'loginok.html'.
   • File monitoring (Sysmon EID 11 / auditd CREATE): new or modified .lua files under the session directory outside normal login flows; KQL: DeviceFileEvents | where FolderPath contains "wftpserver\\Session" and FileName endswith ".lua".
   • Process ancestry (Sysmon EID 1 / EDR): wftpserver.exe or hxxpd.exe as parent of cmd.exe, powershell.exe, wscript.exe, /bin/sh, curl, wget, nc — Splunk: index=edr parent_process_name IN ("wftpserver.exe","hxxpd.exe") process_name IN ("cmd.exe","powershell.exe","sh","bash").
   • Network telemetry (Zeek/Suricata): outbound connections from the FTP host to non-whitelisted destinations, especially reverse-shell ports (4444, 1337, 8080, 443 to unfamiliar destinations) or DNS lookups for Pastebin, Interact.sh or ngrok domains.
   • Windows event logs: EID 4688 with ParentImage matching Wing FTP and NewProcessName of any shell or scripting host; Linux auditd: type=EXECVE events whose ppid belongs to the FTP service.

Detection rules

No NEOSEC detection rule is available for this vulnerability yet.

Classification under NIS2 and CRA

Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

NIS2

NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

Read in glossary

Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).

CRA

The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

Read in glossary

Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.

ISO/IEC 27001

ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

Read in glossary

Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

Description

In Wing FTP Server before 7.4.4. the user and admin web interfaces mishandle '\0' bytes, ultimately allowing injection of arbitrary Lua code into user session files. This can be used to execute arbitrary system commands with the privileges of the FTP service (root or SYSTEM by default). This is thus a remote code execution vulnerability that guarantees a total server compromise. This is also exploitable via anonymous FTP accounts.

Source: pwn.watch, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)

Vendors and products

• Wing FTP Server Wing FTP Server

Weakness classes (CWE)

• CWE-158Improper Neutralization of Null Byte or NUL Character

  Variant

  The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.

  Entry at MITRE CWE-158

References & sources

• wftpserver.comProduct
• rcesecurity.com2025/06/what-the-null-wing-ftp-server-rce-cve-2025-47812Exploit, Third-party advisory
• vicarius.iovsociety/posts/cve-2025-47812-mitigation-script-remote-code-exe…Mitigation, Third-party advisory
• vicarius.iovsociety/posts/cve-2025-47812-detection-script-remote-code-exec…Third-party advisory
• huntress.comblog/wing-ftp-server-remote-code-execution-cve-2025-47812-explo…Third-party advisory, Exploit, Third-party advisory
• cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2025-47812government-resource, US government resource
• pwn.watchpwn.watch: Wing FTP Server: Improper Neutralization of Null Byte or NUL Character Vulnerabilitypwn-watch
• wftpserver.comWing FTP Server advisory: Wing FTP Serverpwn-watch
• NVD (NIST)NVD: CVE-2025-47812pwn-watch
• cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch