CriticalCVE-2023-40044

    WS_FTP Server Ad Hoc Transfer Module .NET Deserialization Vulnerability (CVE-2023-40044)

    Published In CISA KEV since Sources: SingCERT, CVE.org, pwn.watch

    What is affected, what to do

    An authenticated attacker can exploit a deserialization vulnerability in the Ad Hoc Transfer module of Progress WS_FTP Server versions prior to 8.7.4 and 8.8 to 8.8.2 to execute remote commands on the underlying operating system, resulting in remote code execution (RCE). This vulnerability is actively exploited in ransomware campaigns, indicating a high level of urgency for mitigation. Affected products include specific versions of the WS_FTP Server. Immediate patching to version 8.7.4 or 8.8.2 is necessary to address this critical security issue.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Progress Software WS_FTP Server to version 8.8.2, Progress Software WS_FTP Server to version 8.7.4. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Progress Software WS_FTP Server lt 8.8.0..8.8.2
    • Progress Software WS_FTP Server lt 8.7.0..8.7.4
    Fixed in
    • Progress Software WS_FTP Server 8.8.2
    • Progress Software WS_FTP Server 8.7.4

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    10.0

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    10.0

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: SingCERT, CVE.org, pwn.watch

    90.4 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.80

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    258.20 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    10.0 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    10.0
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    90.4 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.80
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 3 February 2025
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-502

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This CVE is on KEV because it is network-reachable without authentication, grants direct remote code execution with the privileges of the WS_FTP service, and was weaponised by ransomware operators (CISA known-ransomware flag) within days of disclosure through mass internet scans. The attack profile mirrors the 2023 MOVEit campaign: internet-exposed managed-file-transfer servers holding sensitive supplier and partner data are the prime target, with mid-market and KRITIS operators handling third-party exchanges particularly exposed. Exploitation likelihood is among the highest of any CVE currently tracked — treat as P1/emergency patch whenever WS_FTP is present, regardless of whether the instance appears internal or external, since internal pivot chains have been documented.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch now: upgrade WS_FTP Server to 8.7.4 (8.7 branch) or 8.8.2 (8.8 branch) or later. Fixes are published in the Progress advisory of 27 Sept 2023 — download from the Progress Community portal.
      • If patching within hours is not feasible, disable the Ad Hoc Transfer module via the WS_FTP Configuration Manager (removes the vulnerable .NET deserialization path) and restart the IIS site.
      • Block management and transfer endpoints at the perimeter (typically TCP/80, TCP/443, TCP/21, TCP/990 plus the configured admin port). Allow access only via VPN or IP allowlist until the patch is verified.
      • Run forensic triage on every WS_FTP host: review IIS logs, the wftpsvc directories and the WFTPServer process tree for ysoserial.net gadgets and unexpected w3wp.exe child processes. Any hit → isolate and treat as compromised.
      • Rotate the WS_FTP service account, local admin credentials, SMTP/DB credentials stored in the configuration and TLS certificates if exploitation traces exist or the audit window contains gaps.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: place WS_FTP in a dedicated DMZ VLAN with tight egress filtering — in particular block outbound traffic from w3wp.exe and WFTPServer.exe to arbitrary destinations to prevent C2 callbacks.
      • WAF or reverse proxy in front of WS_FTP: block or alert on POST requests to /AHT/AhtApi/*, /AHT/*.aspx, and multipart bodies containing __VIEWSTATE or base64-encoded BinaryFormatter headers (AAEAAAD/////).
      • Enable IPS signatures: Snort/Suricata rules for CVE-2023-40044 (e.g. ET 2048026, 2048027) and vendor coverage from Palo Alto, Fortinet or Cisco Talos.
      • Endpoint hardening: enable Microsoft Defender ASR rules that block script/child-process spawning from IIS worker processes. Add an AppLocker/WDAC rule denying w3wp.exe the ability to launch shells or LOLBins (certutil, bitsadmin, mshta).
      • Least privilege: run the WS_FTP service as a non-privileged local account (ideally a gMSA), never as domain admin or local admin. Avoid cached admin sessions on the host.
      • Verify offline backups of configuration and TLS keys — ransomware operators abusing this bug class routinely weaponise file-transfer servers as initial access.

    3. Runbook step 3

      Detection rules

      • Sysmon EID 1 / EDR process tree: w3wp.exe spawning cmd.exe, powershell.exe, rundll32.exe, regsvr32.exe or certutil.exe is highly suspicious on a WS_FTP host. KQL: DeviceProcessEvents | where InitiatingProcessFileName == "w3wp.exe" and FileName in ("cmd.exe","powershell.exe","rundll32.exe").
      • IIS access logs: POST requests to /AHT/AhtApi/postAuthUser or /AHT/* with unusually large Content-Length (> 5000 bytes) and user agents such as python-requests or empty. Splunk: index=iis cs_uri_stem="/AHT/*" cs_method=POST cs_bytes>5000.
      • Network telemetry (Zeek/Suricata): outbound connections from a WS_FTP host to Pastebin, transfer.sh, raw.githubusercontent.com or non-business IPs immediately after a POST to /AHT/.
      • File-system monitoring: new .aspx, .ashx or .dll files written under C:\Program Files (x86)\Ipswitch\WS_FTP Server\ or any IIS webroot — Sysmon EID 11 with path filter.
      • Windows Security EID 4688 / 4624: new local accounts or interactive logons after suspicious IIS traffic; scheduled-task creation (EID 4698) initiated by the WS_FTP service account.

    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 WS_FTP Server versions prior to 8.7.4 and 8.8.2, a pre-authenticated attacker could leverage a .NET deserialization vulnerability in the Ad Hoc Transfer module to execute remote commands on the underlying WS_FTP Server operating system.

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

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Progress Software CorporationWS_FTP Server
    • 8.7.0 – < 8.7.4
    • 8.8.0 – < 8.8.2
    • 8.7.4
    • 8.8.2
    progressws_ftp_server
    • < 8.7.4
    • 8.8 – < 8.8.2
    • 8.7.4
    • 8.8.2

    Vendors and products

    Weakness classes (CWE)

    • CWE-502Deserialization of Untrusted Data

      Base

      The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

      Entry at MITRE CWE-502

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited
    Reference tagged as exploitassetnote.io (opens in a new tab)PoC (publicly reported)reported, not verified—
    Packet StormProgress Software WS_FTP Unauthenticated Remote Code Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • progress.comws_ftpProduct, Product
    • community.progress.comVendor advisory: Progress WS_FTP ServerVendor advisory, Vendor advisory, pwn-watch
    • theregister.com2023/10/02/ws_ftp_updatePress coverage, Third-party advisory
    • rapid7.comblog/post/2023/09/29/etr-critical-vulnerabilities-in-ws_ftp-ser…Broken link, Third-party advisory
    • attackerkb.comtopics/bn32f9sNax/cve-2023-40044Third-party advisory
    • censys.comcve-2023-40044Third-party advisory
    • assetnote.ioresources/research/rce-in-progress-ws-ftp-ad-hoc-via-iis-http-m…Exploit, Third-party advisory
    • packetstormsecurity.comfiles/174917/Progress-Software-WS_FTP-Unauthenticated-Remote-Co…Exploit, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-40044government-resource, US government resource
    • pwn.watchpwn.watch: Progress WS_FTP Server: Deserialization of Untrusted Data (CVE-2023-40044)pwn-watch
    • NVD (NIST)NVD: CVE-2023-40044pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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