> For the complete documentation index, see [llms.txt](https://cortex-docs.paloaltonetworks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cortex-docs.paloaltonetworks.com/analytics-alerts/alerts-by-name/suspicious-dns-traffic.md).

# Suspicious DNS traffic

### Synopsis

| Field                | Value                                                                                                       |
| -------------------- | ----------------------------------------------------------------------------------------------------------- |
| Activation Period    | 14 Days                                                                                                     |
| Training Period      | 30 Days                                                                                                     |
| Test Period          | 10 Minutes                                                                                                  |
| Deduplication Period | 1 Hour                                                                                                      |
| Required Data        | <p>Requires one of the following data sources:<br>Palo Alto Networks Firewall traffic Logs OR XDR Agent</p> |
| ATT\&CK Tactic       | Command and Control (TA0011), Exfiltration (TA0010)                                                         |
| ATT\&CK Technique    | Application Layer Protocol (T1071), Exfiltration Over Alternative Protocol (T1048)                          |
| Severity             | Informational                                                                                               |

### Description

10 KB or more were sent encoded in subdomain names during a 10-minute window. All subdomains queried were under a single suspicious domain. DNS tunneling encodes data in DNS queries and responses, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked.

### Attacker's Goals

* DNS tunneling, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked.
* An attacker may also use this protocol to exfiltrated data from the compromised endpoint outside the network.

### Investigative actions

* Verify that the source device or process is not an approved security solution.
* Verify if the DNS query types are non-standard. DNS tunnels use uncommon query types that enable encoding of more data. Examples include: INIT, PRIVATE, NULL, SRV, KEY, and TXT.
* If the affected endpoint is operating Windows, verify that the DNS traffic is coming from svchost.exe and search for other processes that ran when the alert triggered. On Windows, the DNS requests go through svchost.exe.
* Verify the responses per DNS query. Many responses per query may indicate a tool being downloaded.
* Verify the destination domain details and compare the number of endpoints in your network that access the domain over time to see if this is an uncommonly contacted domain.
* Verify the source web-browser traffic to determine if the process was generated by user action, if the user did not initiate the traffic it can be indicative of malicious activity.
* Verify non-DNS traffic to the domain. Any traffic except DNS queries to the destination domain may indicate a legitimate domain and not used solely for command-and-control or data exfiltration.

### Variations

<details>

<summary>Suspicious DNS traffic with a rarely seen domain</summary>

**Synopsis**

| Field             | Value                                                                              |
| ----------------- | ---------------------------------------------------------------------------------- |
| ATT\&CK Tactic    | Command and Control (TA0011), Exfiltration (TA0010)                                |
| ATT\&CK Technique | Application Layer Protocol (T1071), Exfiltration Over Alternative Protocol (T1048) |
| Severity          | Low                                                                                |

**Description**

10 KB or more were sent encoded in subdomain names during a 10-minute window. All subdomains queried were under a single suspicious domain. DNS tunneling encodes data in DNS queries and responses, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked. This domain was rarely seen in this tenant.

**Attacker's Goals**

* DNS tunneling, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked.
* An attacker may also use this protocol to exfiltrated data from the compromised endpoint outside the network.

**Investigative actions**

* Verify that the source device or process is not an approved security solution.
* Verify if the DNS query types are non-standard. DNS tunnels use uncommon query types that enable encoding of more data. Examples include: INIT, PRIVATE, NULL, SRV, KEY, and TXT.
* If the affected endpoint is operating Windows, verify that the DNS traffic is coming from svchost.exe and search for other processes that ran when the alert triggered. On Windows, the DNS requests go through svchost.exe.
* Verify the responses per DNS query. Many responses per query may indicate a tool being downloaded.
* Verify the destination domain details and compare the number of endpoints in your network that access the domain over time to see if this is an uncommonly contacted domain.
* Verify the source web-browser traffic to determine if the process was generated by user action, if the user did not initiate the traffic it can be indicative of malicious activity.
* Verify non-DNS traffic to the domain. Any traffic except DNS queries to the destination domain may indicate a legitimate domain and not used solely for command-and-control or data exfiltration.

</details>

<details>

<summary>Suspicious DNS traffic with a globally rare DNS query length</summary>

**Synopsis**

| Field             | Value                                                                              |
| ----------------- | ---------------------------------------------------------------------------------- |
| ATT\&CK Tactic    | Command and Control (TA0011), Exfiltration (TA0010)                                |
| ATT\&CK Technique | Application Layer Protocol (T1071), Exfiltration Over Alternative Protocol (T1048) |
| Severity          | Low                                                                                |

**Description**

10 KB or more were sent encoded in subdomain names during a 10-minute window. All subdomains queried were under a single suspicious domain. DNS tunneling encodes data in DNS queries and responses, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked. The combination of the DNS queries along with this root domain is globally rare.

**Attacker's Goals**

* DNS tunneling, allowing an attacker to bypass firewalls and proxies to reach his or her command and control server, even when HTTP/S traffic is blocked.
* An attacker may also use this protocol to exfiltrated data from the compromised endpoint outside the network.

**Investigative actions**

* Verify that the source device or process is not an approved security solution.
* Verify if the DNS query types are non-standard. DNS tunnels use uncommon query types that enable encoding of more data. Examples include: INIT, PRIVATE, NULL, SRV, KEY, and TXT.
* If the affected endpoint is operating Windows, verify that the DNS traffic is coming from svchost.exe and search for other processes that ran when the alert triggered. On Windows, the DNS requests go through svchost.exe.
* Verify the responses per DNS query. Many responses per query may indicate a tool being downloaded.
* Verify the destination domain details and compare the number of endpoints in your network that access the domain over time to see if this is an uncommonly contacted domain.
* Verify the source web-browser traffic to determine if the process was generated by user action, if the user did not initiate the traffic it can be indicative of malicious activity.
* Verify non-DNS traffic to the domain. Any traffic except DNS queries to the destination domain may indicate a legitimate domain and not used solely for command-and-control or data exfiltration.

</details>


---

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