CVE-2021-34793
CVE-2021-34793 is a high-severity vulnerability in Cisco Adaptive Security Appliance with a CVSS 3.x base score of 8.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-924.
Key facts
- Severity: High (CVSS 3.x base score 8.6)
- CVSS v2: 5.0
- EPSS exploit prediction: 1% (47th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-924
- Affected product: Cisco Adaptive Security Appliance
- Published:
- Last modified:
Description
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.
Frequently asked questions
- What is CVE-2021-34793?
- 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.
- How severe is CVE-2021-34793?
- CVE-2021-34793 has a CVSS 3.x base score of 8.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
- Is CVE-2021-34793 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2021-34793?
- CVE-2021-34793 primarily affects Cisco Adaptive Security Appliance. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
- How do I fix CVE-2021-34793?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- When was CVE-2021-34793 published?
- CVE-2021-34793 was published on 2021-10-27 and last updated on 2026-06-17.
References
Affected products (11)
- cpe:2.3:a:cisco:adaptive_security_appliance:*:*:*:*:*:*:*:*
- cpe:2.3:a:cisco:firepower_threat_defense:*:*:*:*:*:*:*:*
- cpe:2.3:o:cisco:adaptive_security_appliance_software:*:*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5512-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5505_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5515-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5525-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5545-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5555-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5580_firmware:009.008\(004.025\):*:*:*:*:*:*:*
- cpe:2.3:o:cisco:asa_5585-x_firmware:009.008\(004.025\):*:*:*:*:*:*:*
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