Product:
Junos OS
Summary
An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS). If an SRX Series device configured for DNS processing receives a specifically formatted DNS request, the flowd process will crash and restart, leading to service interruption until recovery.
Details
| Severity | Base Score | CVE |
|---|---|---|
| HIGH | 8.7 | CVE-2026-21920 |
Exploitation
To exploit this vulnerability, an attacker can send a specifically crafted DNS request to an SRX Series device that is configured for DNS processing. This request will trigger the flowd process to crash, resulting in a Denial-of-Service condition. The attacker does not need any authentication or special privileges to perform this action, making it relatively easy to execute.
Affected Products
- Junos OS 23.4 versions before 23.4R2-S5
- Junos OS 24.2 versions before 24.2R2-S1
- Junos OS 24.4 versions before 24.4R2
Mitigation
To mitigate this vulnerability, it is recommended to upgrade to the latest versions of Junos OS that are not affected by this issue. Regularly applying security updates and patches can help protect against potential exploits. Additionally, monitoring DNS traffic for unusual patterns may help in identifying and preventing attacks.