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Threats / Cisco / CVE-2026-20131
CVE-2026-20131 · EUVD no mirror located · GCVE no mirror located Verified 2026-06-06

Cisco Secure Firewall Management Center (FMC) vulnerability

Cisco Secure Firewall Management Center contains a deserialization vulnerability in its web management interface allowing unauthenticated remote code execution as root.

Verdict

Today item, not a backlog item.

An unauthenticated remote attacker can exploit unsafe deserialization of untrusted data to execute arbitrary Java code with root privileges on affected FMC instances, enabling full device compromise and lateral network movement.

CISA KEV Yes · 2026-03-193Ransomware use Flagged3EPSS 0.01403 (verify live)4
01

Is it exploitable?

— the evidence, ranked above the score
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-03-19), flagged for known ransomware use.
CISA KEV ↗Confirmed
Probability (EPSS)
EPSS 0.01403 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
FIRST EPSS ↗High
Severity / affected
Affected: Cisco, Secure Firewall Management Center (FMC). Confirm exact fixed builds in the vendor advisory.
NVD ↗Reported
Weakness (CWE)
Mapped to CWE-502 Deserialization of Untrusted Data — weakness family: Injection.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
NVD ↗Reported
WeaknessCWE-502 · Deserialization of Untrusted DataInjection
02

Who’s exploiting it?

— attribution turns risk into urgency
Attribution not established

No threat-actor attribution is established from the public feed 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 board
1

Front door — unauthenticated access narrative 1

Attacker
I craft a malicious serialized Java object and send it to the FMC web management interface without authentication.
Business
The organization's firewall management infrastructure is directly accessible to remote attackers without credential barriers.
2

Keys to the kingdom — privilege/identity takeover narrative 2

Attacker
The vulnerable deserialization handler processes my object and instantiates arbitrary classes, executing my embedded payload.
Business
Attackers gain root-level code execution on the central firewall management platform, the highest-trust security appliance.
3

Lateral reach — past segmentation narrative 3

Attacker
I establish persistence and move laterally through the network using the compromised FMC as a pivot point.
Business
The breach extends from the management layer to protected internal networks, enabling ransomware deployment and data exfiltration at scale.
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’t

Established (cited)

  • KEV listing (CISA)
  • Ransomware-use flag (CISA)
  • EPSS probability (FIRST)
  • CWE weakness mapping (NVD)
  • Catalogued by cisco (CNA)

    • Coverage gaps — stated, not hidden

  • No EUVD / GCVE mirror in feed — single-authority dependency for the identifier.
  • EPSS & exposure are time-varying; verify live at the source.
  • Threat-actor attribution not established from feed data — absence of a name is not absence of compromise.
  • No finder/reporter credit recorded in the public CVE entry — the work behind this find is unattributed.
    • Disclosure & credit2
    Catalogued by ciscoCNA
    Credited with finding itNo finder named in the public CVE record — the work behind this find is unattributed.