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    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.

    Published:Oct 27, 2021
    Last Modified:Aug 11, 2026
    EPS:Oct 27, 2021
    EPSS Score:0.00649
    CVSS Score:8.6

    Affected Products

    Vendor
    Cisco
    Product
    Adaptive Security Appliance
    Vendor
    Cisco
    Product
    Adaptive Security Appliance Software
    Vendor
    Cisco
    Product
    Asa 5505
    Vendor
    Cisco
    Product
    Asa 5505 Firmware
    Vendor
    Cisco
    Product
    Asa 5512-x
    Vendor
    Cisco
    Product
    Asa 5512-x Firmware
    Vendor
    Cisco
    Product
    Asa 5515-x
    Vendor
    Cisco
    Product
    Asa 5515-x Firmware
    Vendor
    Cisco
    Product
    Asa 5525-x
    Vendor
    Cisco
    Product
    Asa 5525-x Firmware
    Vendor
    Cisco
    Product
    Asa 5545-x
    Vendor
    Cisco
    Product
    Asa 5545-x Firmware
    Vendor
    Cisco
    Product
    Asa 5555-x
    Vendor
    Cisco
    Product
    Asa 5555-x Firmware
    Vendor
    Cisco
    Product
    Asa 5580
    Vendor
    Cisco
    Product
    Asa 5580 Firmware
    Vendor
    Cisco
    Product
    Asa 5585-x
    Vendor
    Cisco
    Product
    Asa 5585-x Firmware
    Vendor
    Cisco
    Product
    Secure Firewall Threat Defense

    Exploits

    No exploit reference

    Common Attack Pattern Enumeration and Classification (CAPEC)

    No CAPEC recorded yet

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    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High