How severe is CVE-2021-27104?

CVE-2021-27104 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-27104?

Affected package information for CVE-2021-27104 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-27104?

No fixed version has been published for CVE-2021-27104 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

Is CVE-2021-27104 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2021-27104, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-27104?

CVE-2021-27104 has an EPSS (Exploit Prediction Scoring System) score of 6.4%, placing it in the 91th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

Is CVE-2021-27104 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-27104 (Accellion FTA OS Command Injection Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03. CISA required all US federal civilian agencies to remediate this vulnerability by 2021-11-17. The required action was: Apply updates per vendor instructions. This CVE has been used in known ransomware campaigns. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-27104?

CVE-2021-27104 is classified as OS Command Injection (CWE-78). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-27104?

CVE-2021-27104 affects accellion fta. Check the affected-products list on this page against your deployed version to confirm exposure.

When was CVE-2021-27104 published, and has it been updated?

CVE-2021-27104 was published on February 16, 2021 and was last updated on November 3, 2025. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2021-11-03 — agencies required to remediate by 2021-11-17 · Ransomware

CVE-2021-27104

CRITICAL

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.

Published

Feb 16, 2021

Updated

Nov 3, 2025

Affected

0 pkgs

Patched

None yet

Exploits

2 known

EPSS Exploitation Probability

via FIRST.org ↗

6.4%probability of exploitation in next 30 days

Lower Risk91th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Description

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.

Affected Products

1 product · 1 configurations

Application

ftaaccellion

≤ 9_12_370

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

Accellion FTA 9_12_370 and earlier is affected by OS command execution v…

cisa.govCISANov 2021

Accellion FTA 9_12_370 and earlier is affected by OS command execution v…

hkcert.orgAPIMar 2021

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2021-27104 in your stack?

O3 detects CVE-2021-27104 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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