An improper input validation flaw in Juniper Networks Junos OS and Junos OS Evolved enables an unauthenticated adjacent attacker to send a specific genuine BGP packet over an established BGP session. The packet resets only that session, leading to a denial of service for the routes exchanged over the affected link. Repeatedly sending the packet can sustain the outage until the session reestablishes or the device restarts.

Juniper Networks Junos OS and Junos OS Evolved are impacted. For Junos OS the flaw exists in all releases prior to 25.2R2; the 25.2R2, 25.4R1, and all newer releases contain the fix. For Junos OS Evolved, the issue exists in all releases prior to 25.2R2-EVO; the 25.2R2-EVO, 25.4R1-EVO, and all later releases resolve the vulnerability. Both eBGP and iBGP sessions over IPv4 and IPv6 are affected; versions earlier than 25.2R1 (Junos OS) or 25.2R1-EVO (Junos OS Evolved) are not affected.

The CVSS score of 7.1 reflects moderate to high severity. Because the exploit requires only access to a pre‑established BGP session and no authentication, the threat is realistic for attackers who can become an adjacent BGP neighbor on the network. The EPSS score of < 1% indicates a very low but nonzero probability of exploitation in observed traffic. The vulnerability is not listed in CISA KEV. However, the lack of a workaround and the potential for widespread service interruption make the risk significant. Attackers can trigger repeated BGP resets to sustain a denial of service, compromising network reliability.