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CVE-2026-20248

MEDIUM(6.8)

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

Risk Signal Score27/100 — MITTEL
  • CVSS 6.8 — Mittel
  • Weniger als 24 Stunden alt

Erwähnungen (letzte 60 Tage)

Artikel

Beschreibung

A vulnerability in the DNS over TCP implementation of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the TCP DNS response handler to unexpectedly restart, causing the device to reload. This vulnerability is due to a logic error when parsing a DNS query and tracking the size of the incoming buffers. An attacker could exploit this vulnerability by formatting a crafted reply to a DNS query sent from the targeted device. A successful exploit could allow the attacker to cause the device to reload, causing a denial of service (DoS) condition. Note: The attacker must be able to respond to DNS queries from the device, either by controlling the DNS service or through a machine-in-the-middle attack.

Erkennung & Indikatoren

Ausnutzung

In den geprüften Quellen nicht genannt

Threat-Hunting-Queries

Sentinel/Defender KQL

DeviceNetworkEvents
| where ActionType == "DnsQuery"
| where Protocol == "Tcp"
| where RemotePort == 53
| summarize count() by DeviceName, RemoteIP, InitiatingProcessFileName
| where count_ > 50 // Adjust threshold based on environment to detect unusual high volume TCP DNS queries

Splunk SPL

sourcetype=cisco:asa OR sourcetype=cisco:ftd (eventtype=dns_query OR eventtype=dns_response) transport=tcp | stats count by src_ip, dest_ip, process | where count > 50

Sigma

title: Cisco ASA/FTD TCP DNS DoS Attempt
status: experimental
description: Detects potential denial of service attempts against Cisco ASA/FTD devices via crafted TCP DNS responses.
references:
  - https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-tcpdns-dos-p6dUnjr5
logsource:
  product: cisco
  service: firewall
detection:
  selection:
    event_type: dns_response
    protocol: tcp
    dest_port: 53
  condition: selection
falsepositives:
  - Legitimate high volume TCP DNS traffic (requires tuning)
level: medium

Elastic ES|QL

from network where event.dataset == "cisco.asa" or event.dataset == "cisco.ftd" and network.protocol == "dns" and network.transport == "tcp" and destination.port == 53 | stats count() by source.ip, destination.ip, process.name | where count() > 50

SecBoard-generated · behavioral · requires customization — Von SecBoard erzeugt und nicht in einer Zielumgebung validiert. Vor dem Einsatz an die eigene Protokollierung anpassen.

Referenzen