Threats / Accellion / CVE-2021-27104
CVE-2021-27104
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-09-19
Accellion FTA vulnerability
Accellion FTA contains an OS command injection vulnerability in admin endpoints exploitable via crafted POST requests. The flaw has been actively exploited in ransomware campaigns.
Verdict
Today item, not a backlog item.
An unauthenticated or low-privileged attacker can inject arbitrary OS commands through malformed requests to administrative interfaces, achieving remote code execution and enabling data exfiltration or system compromise as a precursor to ransomware deployment.
CISA KEV Yes · 2021-11-034Ransomware use Flagged4EPSS 0.56686 (verify live)5CVSS 9.8 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: total3
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
23 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03), flagged for known ransomware use.
Probability (EPSS)
EPSS 0.56686 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Accellion, FTA. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-20 Improper Input Validation, CWE-78 OS Command Injection — weakness family: Injection.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 260 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a POST request with embedded shell metacharacters targeting an admin endpoint to bypass input validation.
Business
Attackers gain unauthenticated code execution on the file transfer appliance, establishing initial compromise.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I execute system commands with the privileges of the FTA process to enumerate the environment and exfiltrate sensitive files.
Business
Customer data stored in the appliance is accessed and staged for theft or encryption.
3
Lateral reach — past segmentation narrative 3
Attacker
I deploy ransomware payloads or lateral movement tools to extend control across the victim's network.
Business
Operations are disrupted; ransom demands follow; regulatory and reputational damage compounds data loss.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05
Coverage & confidence
— what we know, and what we don’tEstablished (cited)
Coverage gaps — stated, not hidden
Disclosure & credit2
Catalogued by mitreCNA
Credited with finding itNo finder is named in the public CVE record or the scanned vendor advisory — attribution scoped to the sources checked.
Found an error? Propose a correction.
A correction is a cited counter-claim — it must cite a source,
gets reviewed by a second human, and is never auto-applied. See the
correction convention and our identity
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