CriticalCVE-2021-27103

    Accellion FTA Server-Side Request Forgery (SSRF) Vulnerability (CVE-2021-27103)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    An attacker can gain unauthorized access to internal systems through a Server-Side Request Forgery (SSRF) vulnerability in Accellion FTA 9_12_411 and earlier versions. This vulnerability allows the execution of malicious code via a crafted POST request to wmProgressstat.html. It is actively exploited in ransomware campaigns since 2021. All versions up to and including 9_12_411 are affected. An immediate update to FTA_9_12_416 or later is necessary to mitigate the risk.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Accellion FTA to version 9_12_416. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Accellion FTA lt *..9_12_416
    Fixed in
    • Accellion FTA 9_12_416

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    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    11.4 %

    EPSS score

    Elevated — model estimates 10-50% exploitation likelihood.

    Source: FIRST EPSS, percentile 96.0

    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
    247.71 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.

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    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.

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    9.8 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
    9.8
    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“.

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    11.4 %
    Elevated — model estimates 10-50% exploitation likelihood.
    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.

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    96.0
    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.

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    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 · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 27 May 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-918

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction. It formed one link in a chained campaign against Accellion FTA in which attackers planted webshells and stole confidential data at scale. CISA flags it for known ransomware use, consistent with data-theft extortion. Typical victims are organisations that exchange sensitive files with outside parties: government, law firms, finance, healthcare and universities. Treat any internet-exposed, unpatched FTA instance as top priority and assume compromise. Retiring this legacy product is the only durable fix.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Establish exposure: Inventory every Accellion FTA instance using the asset register, Shodan/Censys sweeps of your own IP ranges and certificate CNs. Treat any instance on 9_12_411 or earlier as potentially compromised, not merely vulnerable.
      • Patch or pull the plug: Upgrade immediately to FTA_9_12_416 or later. Accellion FTA is a legacy product with no long-term vendor support. If you cannot upgrade within hours, block external access on TCP/443 and TCP/80 or take the appliance offline. Open a change to migrate to a supported platform.
      • Preserve evidence before rebuilding: Take a forensic image or VM snapshot before patching or shutdown. Secure web-server logs, database dumps and the web-root filesystem. CVE-2021-27103 was chained with CVE-2021-27101 (SQLi), CVE-2021-27102 and CVE-2021-27104 (OS command execution), so hunt for traces of all four.
      • Rotate credentials: Reset every account stored on the FTA, plus admin passwords, API/OAuth keys, LDAP/AD bind accounts and SMTP credentials. Do the same for credentials of internal systems the FTA could reach via SSRF.
      • Check notification duties: If there are signs of data exfiltration, the NIS2 early-warning deadline (24 h to your CSIRT/national authority) and the GDPR Art. 33 deadline (72 h) are running. Bring in the DPO and legal early, because FTA is typically used to exchange confidential files with third parties.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Host the FTA in a DMZ with no route into the internal network. Apply default-deny egress on the appliance and allowlist only required destinations (e.g. SMTP relay, AD on specific ports). This removes the SSRF's value as a pivot to internal services and cloud metadata endpoints (169.254.169.254).
      • WAF/reverse proxy: Block externally sourced POSTs to /wmProgressstat.html. Also filter document_root.html (the CVE-2021-27101 SQLi target) and any unexpected .php paths in the web root. Suricata/Snort idea: alert http $EXTERNAL_NET any -> $FTA_SERVERS any (msg:"Accellion FTA SSRF wmProgressstat"; http.method; content:"POST"; http.uri; content:"/wmProgressstat.html"; nocase; sid:...;).
      • Access restriction: Expose the web interface only via VPN or an IP allowlist of known partners. Never leave the admin interface internet-reachable.
      • Hardening/integrity: Deploy file-integrity monitoring (AIDE or EDR) on the web root and configuration directories. Reduce the web-server process's write permissions to the bare minimum.
      • IAM/least privilege: Strip the FTA's AD service accounts down to minimal rights, with no Domain Admin and no interactive logon. Give external user accounts short expiry periods.

    3. Runbook step 3

      Detection rules

      • Web-server access log: POSTs to wmProgressstat.html with unusual parameters or URL values pointing to internal IPs or localhost. SPL: index=web host=fta* method=POST uri_path="*wmProgressstat.html*" | stats count by src_ip, uri_query.
      • Webshell indicators: New or modified files in the web root, especially about.php (the DEWMODE webshell seen in the FTA campaigns), and requests to it carrying parameters such as dwn= or fn=. Sigma shape: logsource: webserver; detection: cs-uri-stem|endswith: '/about.php' and cs-uri-query|contains: 'dwn='.
      • Outbound network telemetry (Zeek/firewall): FTA connections to internal subnets, the cloud metadata service or unknown external hosts, plus large outbound transfers (exfiltration). Zeek: filter conn.log on id.orig_h == FTA_IP && id.resp_h in RFC1918 && !allowlist.
      • Linux auditd / process ancestry: The web-server process (httpd/php) spawning shells, wget, curl, perl or python. This points to chaining with CVE-2021-27104. Audit rule: -a always,exit -F arch=b64 -S execve -F uid=<webuser> -k fta_exec.
      • Application/database logs: Bulk downloads, newly created admin accounts and SQL errors tied to document_root.html in the same time window as the SSRF requests.

    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

    Accellion FTA 9_12_411 and earlier is affected by SSRF via a crafted POST request to wmProgressstat.html. The fixed version is FTA_9_12_416 and later.

    Source: NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), 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
    accellionfta
    • < 9_12_416
    • 9_12_416

    Vendors and products

    Weakness classes (CWE)

    • CWE-918Server-Side Request Forgery (SSRF)

      Base

      The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

      Entry at MITRE CWE-918

    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

    References & sources

    • accellion.comproducts/ftax_refsource_MISC, Product
    • github.comaccellion/CVEs/blob/main/CVE-2021-27103.txtx_refsource_MISC, Broken link, Product
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27103government-resource, US government resource
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