CVE-2021-27101: Accellion FTA SQL Injection Vulnerability

CVE-2021-27101 is a SQL injection vulnerability in Accellion FTA. Attackers can abuse it by sending a crafted Host header in a request to document_root.html, which can let them interfere with backend database queries. This matters because Accellion FTA is used to move and share files; successful abuse can expose sensitive data and has been tied to ransomware activity. Confirm all product and fix details against the vendor advisory.

How it works

The flaw falls under CWE-89 (SQL injection) and CWE-138 (improper neutralization of special elements). In simple terms, the application does not adequately separate untrusted input from SQL statements. An attacker supplies a malicious Host header when requesting document_root.html. If that value is incorporated into a database query without proper validation or parameterization, the attacker can alter the query’s meaning.

At a technical level this can allow unauthorized reads, writes, or other database operations depending on the privileges of the application’s database account. Exact query structure, injectable parameters, and resulting impact are not detailed in the public summary; treat any deeper exploit mechanics as unconfirmed until verified against the vendor advisory and your own testing in a controlled environment. Do not assume blind or time-based techniques, stacked queries, or specific payloads without evidence from your logs or the advisory.

Am I affected? How to find it in your systems

Accellion FTA is typically deployed as an on-premises or managed file-transfer appliance or server used by enterprises to exchange large or sensitive files with partners and internal users. Inventory any hosts, virtual machines, or appliances running Accellion FTA, including older or forgotten instances in DMZs, partner zones, or backup environments.

• Search asset management, CMDB, and vulnerability-scan data for “Accellion,” “FTA,” or related service banners and TLS certificates.
• Review network diagrams and firewall rules for systems that accept inbound HTTPS (or other FTA ports) from the internet or broad internal networks.
• Check software inventory and package lists on candidate hosts; compare installed versions and build numbers to the fixed releases named in the vendor advisory. Public detail on exact affected version ranges is limited here—confirm directly with the advisory.
• Inspect web-server or application logs for requests to document_root.html that carry unusual or non-standard Host headers, especially from unexpected source IPs. Look for spikes in database errors, unexpected query patterns, or anomalous file-access activity following such requests.
• If you have WAF, reverse-proxy, or IDS logs, search for the same URI and header anomalies. Absence of obvious log hits does not prove safety; the vulnerability may have been probed or exploited before logging was adequate.

How to remediate

Patch first. Apply the updates provided by the vendor exactly as described in their advisory and in line with CISA’s required action: “Apply updates per vendor instructions.” Schedule the upgrade in a maintenance window, take a verified backup, and validate that the FTA service and dependent workflows still function after the update.

After patching, harden the installation for this class of weakness:

• Ensure the application uses parameterized queries or prepared statements for any remaining custom or integrated database access; remove dynamic SQL that concatenates request headers or other untrusted input.
• Run the FTA database account with least privilege—no unnecessary DDL or administrative rights.
• Restrict management and file-transfer interfaces to trusted networks or VPN-only access; disable any unused web endpoints.
• Enable and retain detailed application, web-server, and database audit logging; forward logs to a central SIEM.
• Re-scan the host with an authenticated vulnerability scanner and confirm the CVE is reported as remediated.

If you can't patch immediately

Reduce exposure until the vendor update can be applied:

• Segment the FTA system: place it behind a strict firewall or reverse proxy that allows only required source IPs and ports; block direct internet access if business needs permit.
• Virtual patching: deploy WAF or reverse-proxy rules that reject or sanitize abnormal Host headers and that specifically watch for requests to document_root.html. Tune to avoid breaking legitimate clients; monitor for false positives.
• Disable or restrict the affected functionality if the product allows it without breaking critical file-transfer paths—confirm the exact configuration knobs in vendor documentation.
• Increase monitoring: alert on any request to document_root.html, on Host-header values that do not match expected hostnames, and on unusual database or file-system activity originating from the FTA process.
• Tighten authentication and session controls on the appliance and rotate any credentials that the FTA service uses to reach backend storage or directories.

These steps only buy time; they do not replace the vendor patch.

If your data may have been exposed

This vulnerability has been exploited in the wild and is associated with ransomware operations. If your Accellion FTA instance was unpatched and reachable, treat it as a potential breach: isolate the system, preserve logs and disk images, and begin incident-response procedures including credential rotation and review of files that transited the appliance. Determine whether sensitive data left the environment and notify stakeholders according to your policies and legal requirements. You can also run a free exposure scan of your email addresses against known breach data sets to see whether associated credentials or personal information have appeared in prior incidents, then force password resets and enable multi-factor authentication where needed.