CVE-2026-102023 in Junos OS Evolved
Summary
by MITRE • 10/14/2026
A Reachable Assertion vulnerability in fwstatsd of Juniper Networks Junos OS Evolved allows an authenticated network attacker to cause a denial of service via an SNMP firewall-counter MIB query when at least one firewall counter is configured.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 10/14/2026
The identified security flaw resides within the fwstatsd component of Juniper Networks Junos OS Evolved, specifically manifesting as a reachable assertion error triggered by specific Simple Network Management Protocol operations. This vulnerability allows an authenticated network attacker to induce a denial of service condition against the target device. The attack vector relies on the execution of SNMP firewall-counter MIB queries under conditions where at least one firewall counter is actively configured within the system environment. An assertion failure in this context typically indicates that the software has encountered an unexpected state or input value during runtime, causing the application to halt its normal operation and often resulting in a process crash or restart. In network infrastructure devices like Junos OS Evolved, such crashes can lead to significant service disruption, as critical management processes may need to be restarted by the operating system's watchdog mechanisms, potentially interrupting ongoing monitoring sessions and creating windows of vulnerability during recovery periods.
From a technical perspective, this issue classifies under CWE-617, which denotes Reachable Assertion, indicating that code logic fails to properly validate input or handle edge cases before reaching critical safety checks. The presence of firewall counters is a prerequisite for exploitation, suggesting that the defect lies in how statistical data structures are accessed or processed during SNMP retrieval operations when specific counter states exist. Because authentication is required prior to triggering this vulnerability, it represents an insider threat scenario or a compromise of administrative credentials rather than a remote unauthenticated attack. However, given that network management interfaces often require persistent authenticated sessions for monitoring and configuration tasks, the risk of exploitation remains substantial in environments where credential hygiene is not strictly enforced. The operational impact includes potential instability in network performance monitoring tools that rely on continuous SNMP polling, as repeated crashes or restarts can lead to data loss regarding historical traffic statistics and firewall event logs.
This vulnerability aligns with MITRE ATT&CK technique T1498, Network Denial of Service, specifically the sub-technique related to resource exhaustion via application layer attacks. Although it does not consume bandwidth in a traditional volumetric sense, it exhausts system resources by crashing critical daemons responsible for network statistics collection and reporting. The attacker leverages legitimate SNMP functionality to destabilize the host, effectively achieving availability impairment through software logic errors rather than brute force or flooding techniques. This highlights the importance of robust input validation within management plane components that handle high-frequency queries from monitoring systems such as SolarWinds, PRTG, or custom scripts used for network observability.
Mitigation strategies should prioritize applying vendor-provided patches to update the fwstatsd component and ensure Junos OS Evolved is running a version where this assertion handling has been corrected. In environments where patching cannot be immediately implemented, administrators can reduce exposure by restricting SNMP access through strict Access Control Lists that limit which IP addresses or subnets are permitted to query firewall counter MIBs. Additionally, disabling unnecessary SNMP services if they are not required for network monitoring operations will eliminate the attack surface entirely. Regular auditing of authenticated sessions and enforcing multi-factor authentication for management interfaces further reduces the likelihood of an attacker gaining the necessary credentials to exploit this flaw. Continuous monitoring of system logs for unexpected process restarts or assertion failures can also aid in early detection of attempted exploitation activities, allowing security teams to respond before significant operational disruption occurs.