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NVD / CVE Program· CNA cisco

CVE-2021-34793: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Transparent Mode Denial of Service Vulnerability

Noroxi assessment

Priority: Monitor (action score 34/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.58% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • According to the record, no fixed version is available yet.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

A vulnerability in the TCP Normalizer of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software operating in transparent mode could allow an unauthenticated, remote attacker to poison MAC address tables, resulting in a denial of service (DoS) vulnerability. This vulnerability is due to incorrect handling of certain TCP segments when the affected device is operating in transparent mode. An attacker could exploit this vulnerability by sending a crafted TCP segment through an affected device. A successful exploit could allow the attacker to poison the MAC address tables in adjacent devices, resulting in network disruption.

HighCVSS 8.6 · v3.1—No exploit No fix recorded
Published
Oct 27, 2021
Updated
Aug 11, 2026
EPSS
0.5% · 48th percentile

Report tools

JSON

Action score

34

Monitor

Low priority for now.

CVSS
34 / 40 · 8.6 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
8.6
CNA · cisco
8.6
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-34793

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
ciscoadaptive security appliance
ciscosecure firewall threat defense
ciscoadaptive security appliance software
ciscoasa 5512-x firmware
ciscoasa 5512-x
ciscoasa 5505 firmware
ciscoasa 5505
ciscoasa 5515-x firmware
ciscoasa 5515-x
ciscoasa 5525-x firmware
ciscoasa 5525-x
ciscoasa 5545-x firmware

and 7 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • cisco adaptive security appliance software9.9.0 and later · before 9.12.4.29
  • cisco adaptive security appliance software9.13.0 and later · before 9.14.3.9
  • cisco adaptive security appliance software9.15.0 and later · before 9.15.1.17
  • cisco adaptive security appliance software9.16.0 and later · before 9.16.2.3

Versions reported by the vendor

Affected version ranges reported by the assigning authority (cisco). Independent of NVD's CPE analysis and usually ahead of it.

  • Cisco Cisco Adaptive Security Appliance (ASA) Software

    • n/aaffected

Same product

cisco: all records

Other highest-scoring records for the same primary product.

  • CVE-2020-3572Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SSL/TLS Session Denial of Service Vulnerability
    35Monitor
  • CVE-2020-3436Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services File Upload Denial of Service Vulnerability
    35Monitor
  • CVE-2020-3304Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Web Services Denial of Service Vulnerability
    35Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2021-34790Oct 27, 2021 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Application Level Gateway Bypass Vulnerabilities
    21Monitor
  • ← EarlierCVE-2021-34791Oct 27, 2021 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Application Level Gateway Bypass Vulnerabilities
    21Monitor
  • Later →CVE-2021-40117Oct 27, 2021 · Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software SSL/TLS Denial of Service Vulnerability
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-924 · Improper Enforcement of Message Integrity During Transmission in a Communication Channel

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records