CVE-2026-101979 in Junos OS
Summary
by MITRE • 10/15/2026
A Stack-based Buffer Overflow vulnerability in the authd Juniper Networks Junos OS and Junos OS Evolved allows a network attacker with SNMP read access to execute code with root privileges or cause a denial of service via a specific SNMP packet, when SNMP and AAA are enabled.
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Analysis
by VulDB Data Team • 10/15/2026
The identified vulnerability represents a critical security flaw within the authentication daemon, authd, of Juniper Networks Junos OS and Junos OS Evolved platforms. This stack-based buffer overflow arises from improper boundary checking during the processing of Simple Network Management Protocol (SNMP) packets. The attack vector specifically requires an adversary to possess SNMP read access on the target device, a privilege level that is often granted for routine network monitoring and management purposes. When both SNMP services and Authentication, Authorization, and Accounting AAA frameworks are enabled concurrently, the system becomes susceptible to exploitation through crafted SNMP requests designed to exceed expected buffer limits within the authd process memory space.
From a technical perspective, this flaw falls under CWE-121 Stack-based Buffer Overflow, where input data is copied into a fixed-size stack buffer without adequate validation of its length. By sending a specifically constructed SNMP packet containing an oversized or malformed payload, an attacker can overwrite adjacent memory locations on the call stack. This overwriting typically targets return addresses or function pointers stored in the stack frame. If successful, this manipulation allows for arbitrary code execution with root privileges because authd operates at a high privilege level to manage user authentication and session control. Alternatively, if the overflow corrupts critical program state without achieving precise control flow hijacking, it results in application crashes leading to denial of service conditions affecting network management capabilities.
The operational impact of this vulnerability is severe due to its potential for remote code execution with elevated privileges. An attacker who exploits this flaw gains full administrative control over the affected device, enabling them to modify routing tables, intercept traffic, install persistent backdoors, or pivot into other segments of the internal network. In scenarios where exploitation leads only to a crash, the impact is still significant as it disrupts SNMP-based monitoring and management tools, potentially masking further malicious activities by disabling visibility mechanisms. The requirement for SNMP read access means that organizations must carefully audit their SNMP community strings and access control lists to ensure that such privileges are not unnecessarily granted to untrusted or low-privilege entities.
Mitigation strategies should focus on both immediate remediation and long-term architectural hardening. Juniper Networks has released software updates addressing this specific buffer overflow; therefore, applying the latest security patches for Junos OS and Junos OS Evolved is the primary corrective action. Administrators must also enforce strict access control policies by restricting SNMP read access to only trusted management stations using IP-based ACLs or firewall rules. Disabling unnecessary SNMP services if they are not required for operations further reduces the attack surface. Additionally, implementing network segmentation ensures that even if an attacker gains initial foothold via compromised credentials, lateral movement toward critical infrastructure devices is hindered.
This vulnerability aligns with MITRE ATT&CK technique T1078 Valid Accounts, as exploitation relies on legitimate SNMP access rights being abused for unauthorized purposes. It also relates to CWE-20 Improper Input Validation and CWE-787 Out-of-bounds Write in the context of memory corruption. Security teams should monitor network traffic for anomalous SNMP packet sizes or frequencies that may indicate probing attempts. Regular vulnerability scanning focused on management plane services, combined with strict adherence to least privilege principles regarding SNMP configurations, is essential to prevent exploitation of this and similar stack-based overflow vulnerabilities across enterprise networks.