CriticalCVE-2021-27101

    Accellion FTA SQL Injection Vulnerability (CVE-2021-27101)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    Accellion FTA 9_12_370 and earlier is affected by SQL injection via a crafted Host header in a request to document_root.html. The fixed version is FTA_9_12_380 and later.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Accellion FTA lte *..9_12_370

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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

    6.0 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 93.3

    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
    243.65 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.

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    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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    6.0 %
    Moderate — model estimates 1-10% 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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    93.3
    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.

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    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 27 May 2025

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication or user interaction. It is the entry point of an attack chain that ends in a webshell and bulk theft of sensitive files. CISA flags its use in ransomware and extortion campaigns. Typical targets were organisations using FTA for partner file exchange, including government bodies, law firms, healthcare, finance, and manufacturing. Exploitation likelihood is well above average. Because the product is unsupported, any FTA instance still exposed to the internet should be scored as critical and presumed breached: isolate it, run forensics, and replace it.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Find every Accellion FTA instance using your asset inventory, external attack-surface scans, and certificate-transparency searches for FTA hostnames. Treat any internet-facing instance on 9_12_370 or earlier as presumed compromised.
      • Isolate: Cut the appliance off at the perimeter by blocking HTTPS/443 and any management ports. Before changing anything, capture forensic evidence: a VM snapshot or disk image, Apache and application logs, and a database dump.
      • Patch: Upgrade to at least FTA_9_12_380. FTA is a legacy product whose vendor support has ended, so patching only buys time and migration to a supported platform is mandatory. For the latest build: patch available from the vendor — check the vendor advisory for the current version.
      • Hunt for compromise: Look for webshells in the web root, especially unknown or recently modified files under /home/seos/courier/ (e.g. about.html). Also check for unexpected changes made via sftp_account_edit.php.
      • Rotate credentials: Reset every secret stored on or used by FTA. This covers FTA admin and user accounts, LDAP/AD bind accounts, API/OAuth keys, and SFTP credentials.
      • Assess notification duties: FTA typically carries personal or confidential data. Bring in your DPO (GDPR Art. 33, 72-hour deadline) and prepare the 24-hour NIS2 early warning to your national CSIRT.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Expose FTA only behind a reverse proxy or VPN, with no direct internet access to the appliance. Apply default-deny egress so the appliance can reach only the destinations it needs.
      • WAF/reverse proxy: Block requests to /courier/document_root.html. Also drop any request whose Host header does not exactly match the expected FQDN or contains SQL metacharacters (', ", --, /*, UNION, SELECT, ;). Enforce a strict host-header allowlist at the proxy.
      • IPS signature: Deploy a Suricata/Snort rule that matches http.uri containing document_root.html together with SQL patterns in http.host. Add an alert for sftp_account_edit.php access from non-admin source networks.
      • Application hardening: Restrict admin endpoints (the /courier/ admin area and sftp_account_edit.php) to the admin VLAN via IP allowlist. Disable any features you do not use.
      • IAM/least privilege: Limit the directory bind account to read-only. Keep file retention on FTA short so less data is available to exfiltrate.
      • Decommission: Set a firm migration deadline. An unsupported file-transfer appliance is not an acceptable long-term residual risk.

    3. Runbook step 3

      Detection rules

      • Web access logs (FTA Apache or reverse proxy): Hunt for requests to document_root.html that carry an abnormal Host header. SPL: index=web uri_path="*document_root.html" | regex host="(?i)('|%27|union|select|--)"
      • Webshell activity: Look for requests to /courier/about.html with parameters such as dwn= or fn=, and for large responses (file downloads) to external IPs. KQL: CommonSecurityLog | where RequestURL has "/courier/about.html" and RequestURL has_any ("dwn=","fn=")
      • File integrity: Use auditd or FIM to catch new or modified .html/.php files under /home/seos/courier/. auditd rule: -w /home/seos/courier/ -p wa -k fta_webroot
      • Process ancestry: Flag httpd spawning shells or interpreters (sh, bash, perl, python). Also flag archivers (zip, tar) touching the data store.
      • Network telemetry (Zeek/Suricata): Watch for outbound volume from the FTA IP above baseline and for HTTPS sessions with response-heavy byte ratios to previously unseen client IPs. Zeek: filter conn.log on the FTA IP where resp_bytes exceeds baseline.

    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_370 and earlier is affected by SQL injection via a crafted Host header in a request to document_root.html. The fixed version is FTA_9_12_380 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_370
    • —

    Vendors and products

    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, Vendor advisory
    • github.comaccellion/CVEs/blob/main/CVE-2021-27101.txtx_refsource_MISC, Broken link, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-27101government-resource, US government resource
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