⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Critical · CVSS 10 ⚠ ACTIVELY EXPLOITED — CISA KEV

How to Fix CVE-2023-40044: Deserialization RCE in WS_FTP Server

Other vulnerabilities in the same area that are worth patching alongside this one:

*By Sai Kiran Pandrala*

⚡ At a glance
SeverityCVSS 10 - Critical
Actively exploited?Yes, listed in CISA KEV (added 2023-10-05)
Affected8.8.0 < 8.8.2, 8.7.0 < 8.7.4
Fixed inSee vendor advisory
Type (CWE)CWE-502: Deserialization of Untrusted Data
Patch immediately. CISA's KEV listing means active exploitation is confirmed. Federal agencies must remediate by 2023-10-26.

What is CVE-2023-40044?

CVE-2023-40044 is an unsafe deserialization in WS_FTP Server. The application accepts attacker-controlled serialized objects and reconstructs them without validating their type, so a crafted payload triggers code execution inside the running process. Unauthenticated remote code execution is the typical impact. Vendor description: In WS_FTP Server versions prior to 8.7.4 and 8.8.2, a pre-authenticated attacker could use a .NET deserialization vulnerability in the Ad Hoc Transfer module to execute remote commands on the underlying WS_FTP Server operating system.

Why this CVE matters

Deserialization bugs are a favorite of ransomware operators because they convert a single HTTP request into full code execution on the target host. Public proof-of-concept code for this CVE class typically appears within days of disclosure, and weaponized exploits follow shortly after.

For deployments of WS_FTP Server that have been exposed to the public internet during the disclosure window, the operating assumption should be that scanning has already happened. Confirmed in-the-wild exploitation makes that assumption mandatory, not cautious. Patching closes the door; log review and credential rotation close out the rest of the response.

Am I affected?

You are affected if your installation matches any of these version ranges:

Check your installed version against the list above. If you cannot determine the version, treat the system as affected and follow the upgrade path below.

Open WS_FTP Server's About dialog or run the vendor-documented version-check command. Compare the result against the affected ranges in the advisory.

How to fix CVE-2023-40044

  1. Read the vendor advisory in full: https://www.progress.com/ws_ftp
  2. Upgrade WS_FTP Server to the patched build listed in the vendor advisory.
  3. Back up the configuration (and database, where applicable) before upgrading.
  4. Rotate any credentials, API keys, or session tokens that the vulnerable service touched. An unauthenticated RCE-class flaw means anything the process could see should be treated as exposed.
  5. Apply the patch in a maintenance window. For HA pairs, upgrade the standby node first, fail over, then upgrade the former primary.
  6. Restart the affected service so the patched binary loads, then verify the new version (see verification section).

Apply the Microsoft security update


# The exact KB number is listed in the Microsoft advisory: https://community.progress.com/s/article/WS-FTP-Server-Critical-Vulnerability-September-2023
# Confirm the patch is missing on this host
Get-Hotfix -Id <KB-from-advisory> -ErrorAction SilentlyContinue

# Install the rollup that ships the fix
Install-Module PSWindowsUpdate -Force -SkipPublisherCheck
Import-Module PSWindowsUpdate
Get-WindowsUpdate -KBArticleID <KB-from-advisory> -AcceptAll -Install -AutoReboot

# Verify the patch is now present
Get-Hotfix -Id <KB-from-advisory>


# Inventory missing patches across a Windows fleet via Ansible (winrm)
ansible windows -m win_updates -a "category_names=SecurityUpdates state=installed"

Verify the fix landed


# 1. Confirm the running version matches the fixed-in version from the advisory:
#    https://community.progress.com/s/article/WS-FTP-Server-Critical-Vulnerability-September-2023
#    Use the platform-specific version probe above.

# 2. Re-scan with your vulnerability scanner (Nessus, Qualys, Tenable, OpenVAS).
#    The scanner should no longer flag CVE-2023-40044 on the patched target.

# 3. Inspect recent service / kernel logs for crash loops or rollback events.
journalctl -u <service> --since "10 minutes ago"
dmesg --since "10 minutes ago"

If you cannot patch immediately

There is no safe runtime mitigation for deserialization flaws beyond removing exposure: block the affected endpoint at a reverse proxy or WAF and restrict access to authenticated, trusted users only. Patch as soon as possible.

How to verify the fix worked

If your installation was internet-reachable during the disclosure window, treat log review as part of the remediation rather than an optional follow-up. Look for unexpected administrator accounts in WS_FTP Server, scheduled tasks or cron jobs you did not create, new files in web-accessible directories, and outbound connections to addresses not in your baseline. Suspicious requests to the vulnerable endpoint immediately followed by successful 200-class responses with unusually large bodies are a strong indicator of exploitation. Because WS_FTP Server sits on CISA's Known Exploited Vulnerabilities catalog for this CVE, defenders should also pull the IOC list from the vendor advisory and from CISA's analysis if one was published.

Frequently asked questions

Is CVE-2023-40044 being exploited in the wild?

Yes. CISA added CVE-2023-40044 to the Known Exploited Vulnerabilities catalog, which means active exploitation has been confirmed by federal observation or credible vendor reporting.

Will a WAF or IDS rule fully mitigate CVE-2023-40044?

No. Network-layer filters can reduce noise and slow opportunistic scanners, but they will not stop a determined attacker. The vendor patch is the only durable fix.

Do I need to assume compromise if my WS_FTP Server was internet-facing and unpatched?

For an unauthenticated RCE-class flaw exposed to the public internet during the known exploitation window, yes. Review logs, rotate credentials the process could access, and look for unexpected accounts, scheduled tasks, or outbound connections.

References

*This guide was assembled from the official vendor advisory, the NVD record, and the CISA KEV catalog entry on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*