Key points
- The flaw is a stack-based buffer overflow in the httpd process, rated critical with a CVSS score of 9.8.
- It affects Junos OS and Junos OS Evolved versions prior to specific service releases in the 23.4, 24.2, 24.4, and 25.2 branches.
- Attackers need no authentication to trigger remote code execution or denial of service via a configured J-Web virtual domain.
Juniper Networks Junos OS and Junos OS Evolved contain a critical vulnerability in their web management interfaces. The issue stems from a stack-based buffer overflow within the httpd process. This flaw allows unauthenticated network attackers to execute remote code or cause denial of service. The vulnerability is present in systems running specific older versions of these operating systems. Organizations using J-Web virtual domains are directly exposed to this risk. The National Vulnerability Database lists the issue as CVE-2026-101983.
In plain English
A buffer overflow occurs when a program writes more data to a memory block than it can hold. In this case, the httpd process, which handles web traffic for the J-Web interface, fails to check input limits. An attacker can send specially crafted requests to this service. Because the flaw is in the web process, the attacker does not need a username or password. They can connect from anywhere on the network. This allows them to take control of the system or crash it entirely.
The background
The vulnerability is classified as CWE-121, a stack-based buffer overflow. It affects the httpd process in both Junos OS and Junos OS Evolved. The National Vulnerability Database records two entries for CVE-2026-101983, with CVSS scores of 9.8 and 9.3. Both ratings are critical. The flaw is triggered via a J-Web virtual domain configuration. This means any virtual domain managed through the web interface is a potential entry point. The issue has been present in versions prior to the specified service releases.
What changes now
Users must identify which versions of Junos OS and Junos OS Evolved they are running. If their version is older than the thresholds listed below, they are vulnerable. Junos OS versions before 23.4R2-S8.13, 24.2R2-S5.5, 24.4R2-S5, and 25.2R2-S2 are affected. Junos OS Evolved versions before 23.4R2-S8.11-EVO, 24.2R2-S5.6-EVO, 24.4R2-S5-EVO, and 25.2R2-S2-EVO are also affected. Upgrading to these or later service releases is required to mitigate the risk. No other workaround is confirmed in the source material.
Who needs to act first
Teams should prioritize systems where the J-Web interface is accessible from untrusted networks. Check which devices have virtual domains configured with web management enabled. These systems face the highest exposure because attackers need no credentials to exploit the flaw. Before applying updates, create full configuration backups of all affected devices. Test the upgrade in a non-production environment to ensure stability. Roll out the fix to internet-facing routers first, then to internal core devices. Monitor system logs for any unusual httpd process behavior during the transition.
Background: Unauthenticated remote code execution
Unauthenticated remote code execution often stems from default credentials, exposed management interfaces, and improper input handling. Fix these by enforcing strict authentication, disabling unused services, validating all inputs, and isolating privileged components from public networks.
Read the full guide: Unauthenticated RCE Mistakes: 7 Errors That Expose Your Systems
What to do and how to stay safe: Juniper Networks
- Audit all Juniper devices to identify those running vulnerable versions of Junos OS or Junos OS Evolved.
- Restrict access to the J-Web interface by blocking external traffic to the httpd ports until updates are applied.
- Verify that virtual domains are not exposing the web management interface to untrusted networks.
- Monitor network traffic for signs of exploitation attempts against the httpd process on affected devices.
Step-by-step guide: 7 Configuration Errors That Expose Systems to Zero-Day Exploits
General security guidance from the Vuln Post newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVE ID for this Juniper vulnerability?
The vulnerability is identified as CVE-2026-101983 in the National Vulnerability Database.
Does this bug require an attacker to log in?
No, the source material states that an unauthenticated network attacker can exploit this flaw.
Which specific versions of Junos OS are affected?
Junos OS versions before 23.4R2-S8.13, 24.2R2-S5.5, 24.4R2-S5, and 25.2R2-S2 are affected.
