CVE-2026-57029 is a missing synchronization vulnerability (CWE-820) in the flow collector handler of Juniper Networks Junos OS Evolved running on QFX Series devices. When the reachability of an sFlow collector changes, the system updates the corresponding next-hop entry. If this update happens simultaneously with the sFlow thread accessing the next-hop data, it causes a race condition leading to a crash of the evo-pfemand process. The crash results in a denial-of-service impacting all traffic forwarding until the process restarts automatically. The vulnerability affects all 23.2 versions, 23.4 versions before 23.4R2-S7-EVO, 24.2 versions before 24.2R2-S5-EVO, 24.4 versions before 24.4R2-S3-EVO, and 25.2 versions before 25.2R2-EVO of Junos OS Evolved on QFX Series.

An adjacent, unauthenticated attacker can cause a denial-of-service by triggering a crash of the evo-pfemand process, which disrupts all traffic forwarding on affected devices until the process automatically restarts. There is no impact to confidentiality or integrity reported.

A patch is available for this vulnerability. Since Junos OS Evolved on QFX Series is a cloud-managed service, the vendor manages remediation for this cloud-hosted service. Users should consult the Juniper Networks advisory for the latest patch and update to fixed versions: 23.4R2-S7-EVO or later, 24.2R2-S5-EVO or later, 24.4R2-S3-EVO or later, and 25.2R2-EVO or later. Applying these updates will mitigate the issue.