Security readout for executives and security teams
Plain-English summary
This flaw can let a remote unauthenticated attacker disrupt networks by abusing Cisco ASA or FTD devices running in transparent mode. The business risk is availability loss: poisoned MAC address tables in nearby devices can interrupt traffic paths and cause network disruption.
Executive priority
Prioritize remediation where transparent-mode Cisco firewalls protect critical or shared network paths. The main business concern is outage or traffic disruption. Urgency is high, but the provided sources do not show active exploitation.
Technical view
CVE-2021-34793 is in the TCP Normalizer handling of certain TCP segments when Cisco ASA or FTD operates in transparent mode. A crafted TCP segment passing through an affected device can poison MAC address tables on adjacent devices, causing denial of service. CVSS is 8.6 high.
Likely exposure
Exposure is likely limited to Cisco ASA or FTD deployments operating in transparent mode, especially inline bridge-style firewall placements. The bundle does not provide affected version ranges, so teams must validate releases against Cisco's advisory.
Exploitation context
The source bundle says exploitation is unauthenticated, remote, and low complexity. It does not cite known active exploitation, and KEV status is false. Treat this as a disruption risk, not a confidentiality or integrity compromise.
Researcher notes
The key condition is transparent mode. The vulnerability affects TCP segment handling in the normalizer and impacts adjacent MAC tables. The bundle lacks version granularity, workaround details, and exploit-in-the-wild evidence; defer to Cisco's advisory for release-specific validation.
Mitigation direction
- Check Cisco's advisory for affected and fixed release guidance.
- Inventory ASA and FTD devices running transparent mode.
- Prioritize remediation for devices on critical network paths.
- Monitor adjacent switching infrastructure for MAC table anomalies.
- Use vendor guidance before changing topology or firewall behavior.
Validation and detection
- Confirm whether ASA or FTD is deployed in transparent mode.
- Map adjacent devices that could receive poisoned MAC table entries.
- Compare software versions against Cisco's advisory.
- Review network monitoring for unexplained disruption around inline firewalls.
- Document business services dependent on affected traffic paths.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CWE-924: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-34793 mapping review
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Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20211027 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Transparent Mode Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Enforcement of Message Integrity During Transmission in a Communication Channel
Improper Enforcement of Message Integrity During Transmission in a Communication Channel represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.