Cyber Resilience

CVE-2021-27104

RCE in Accellion Fta ≤ 9_12_370

CISA KEVActive ExploitationEUVD ExploitedRansomware-linkedRCECommand Injection
Published
16 February 2021
Modified
03 November 2025
KEV Added
03 November 2021
Patch / advisory
View advisory
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.56 99th percentile
Risk Priority 97 floored blend · peak EPSS

Summary

CVE-2021-27104 is a critical-severity OS Command Injection (CWE-78) vulnerability in Accellion Fta. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked in the top 1% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

Accellion FTA versions 9_12_370 and earlier contain an OS command injection vulnerability, tracked as CVE-2021-27104 and assigned CWE-78. The flaw resides in multiple administrative endpoints that process POST requests, allowing arbitrary operating system commands to be executed on the underlying server. The issue carries a CVSS 3.1 base score of 9.8, reflecting network-accessible attack vectors that require no authentication or user interaction.

An unauthenticated remote attacker can submit a specially crafted POST request to the affected admin endpoints and obtain full control over the Accellion FTA appliance, including the ability to read, modify, or delete data and execute further commands on the host. Because the vulnerability does not require credentials, it can be targeted by any party with network reachability to the appliance.

Vendor guidance states that the vulnerability is resolved in FTA version 9_12_380 and later. The affected product page and the Accellion CVE disclosure both direct customers to upgrade to the patched release. The entry also appears in the CISA Known Exploited Vulnerabilities catalog, confirming that the flaw has been observed in active exploitation campaigns.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

Accellion FTA 9_12_370 and earlier is affected by OS command execution via a crafted POST request to various admin endpoints. The fixed version is FTA_9_12_380 and later.

CWE(s)
CWE-78
KEV Date Added
03 November 2021

Related Threats

MITRE ATT&CK Enterprise Techniques

T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
T1059.003 Windows Command Shell Execution
Adversaries may abuse the Windows command shell for execution.
attack.mitre.org →
T1059.004 Unix Shell Execution
Adversaries may abuse Unix shell commands and scripts for execution.
attack.mitre.org →
T1059.001 PowerShell Execution
Adversaries may abuse PowerShell commands and scripts for execution.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2021-27102Same product: Accellion Ftaboth on KEV
CVE-2021-27103Same product: Accellion Ftaboth on KEV
CVE-2021-27101Same product: Accellion Ftaboth on KEV
CVE-2026-28269Same product class: managed file transfer
CVE-2025-13444Same product class: managed file transfer
CVE-2026-59688Same product class: managed file transfer
CVE-2025-13447Same product class: managed file transfer
CVE-2026-59687Same product class: managed file transfer
CVE-2015-2857Same product class: managed file transfer
CVE-2026-59686Same product class: managed file transfer

Affected Assets

accellion
fta
≤ 9_12_370

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.5
  • V1.2.8
  • V15.2.5

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SC-27 Platform-independent Applications
addresses: CWE-78

Platform-independent apps typically execute inside a managed runtime or sandbox that restricts direct OS command execution, reducing the ability to exploit OS command injection.

SI-10 Information Input Validation
addresses: CWE-78

Validates inputs to block special elements that would alter OS command execution.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

PR.PS-06's SDLC practices directly require secure coding and input handling that blocks command-injection defects, yet the single broad outcome leaves many specific neutralization vectors and verification gaps unaddressed.

PR.PS-02 partial match
prevents

Routine patching/maintenance can remediate known command-injection CVEs in dependencies (partial forward) but does nothing to stop developers from introducing improper neutralization in custom code (none reverse).

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing and code review target insecure use of operating-system command interfaces, catching command-injection flaws introduced during development.

References