A stack‑based buffer overflow exists in the l2cpd process of Juniper Networks Junos OS and Junos OS Evolved. The flaw is triggered by processing LLDP traffic on an interface that has Unified Access Policy enabled. An unauthenticated attacker can supply crafted LLDP frames that overflow a buffer, causing a denial of service or enabling execution of arbitrary code with root privileges. This vulnerability is identified as CWE‑121, which denotes stack buffer overflows.

The issue affects Junos OS and Junos OS Evolved devices running releases older than the patched versions listed in the vendor advisory. For JunOS OS, releases older than 23.2R2‑S7.7, 23.4R2‑S8.13, 24.2R2‑S5.5, 24.4R2‑S5, 25.2R2‑S2, 25.4R1‑S3, 25.4R2, 26.2R1‑S2, 26.2R2, 26.4R1 are vulnerable. Likewise, Junos OS Evolved releases older than 23.2R2‑S7.7‑EVO, 23.4R2‑S8.11‑EVO, 24.2R2‑S5.6‑EVO, 24.4R2‑S5‑EVO, 25.2R2‑S2‑EVO, 25.2X100‑D35‑EVO, 25.4R1‑S3‑EVO, 25.4R2‑EVO, 25.4X300‑D40‑EVO, 26.2R1‑S2‑EVO, 26.2R2‑EVO, 26.4R1‑EVO are also affected. All releases following the patched versions are not vulnerable.

The CVSS score of 8.7 classifies the issue as high severity, with the potential for full root code execution. Although no EPSS score is available, the lack of a KEV listing does not diminish the risk; the vulnerability is exploitable by any networked attacker capable of sending LLDP packets to the target device, and no local authentication is required. The attack vector is likely remote over the network, and successful exploitation would grant the attacker complete control of the device and the ability to disrupt service.