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CVE-2026-57027 Juniper Networks CVE debrief

A Missing Release of Memory after Effective Lifetime vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX Series devices allows an unauthenticated adjacent attacker to cause a Denial-of-Service (DoS). The vulnerability is triggered when sFlow is configured in a Virtual Chassis (VC) scenario with EX4100 Series or EX4400 Series devices. In this scenario, multicast traffic received on one VC member and sent out on another member leads to a memory leak. This memory leak can cause an FPC crash and restart. The leak can be monitored by observing the continuous increase of buffer values in the output of 'show chassis fpc'. This issue affects Junos OS on EX4100 Series and EX4400 devices with specific version ranges.

Vendor
Juniper Networks
Product
Junos OS
CVSS
HIGH 7.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-09
Original CVE updated
2026-07-10
Advisory published
2026-07-09
Advisory updated
2026-07-10

Who should care

Users of Juniper Networks Junos OS on EX4100 Series and EX4400 devices should apply patches to prevent Denial-of-Service (DoS) attacks. System administrators and security teams responsible for these devices need to review the vulnerability details and apply necessary patches or mitigations. Monitoring buffer values using 'show chassis fpc' can help detect potential memory leaks. Restricting access to vulnerable devices can also help prevent exploitation.

Technical summary

The vulnerability exists in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX Series devices. An unauthenticated adjacent attacker can exploit this vulnerability to cause a Denial-of-Service (DoS). The exploit involves multicast traffic in a Virtual Chassis (VC) scenario with EX4100 Series or EX4400 Series devices. The memory leak caused by the vulnerability can be monitored using the 'show chassis fpc' command. Affected Junos OS versions include all versions before 23.2R2-S7, 23.4 versions before 23.4R2-S7, 24.2 versions before 24.2R2-S4, and 24.4 versions before 24.4R2.

Defensive priority

Apply patches immediately, monitor buffer values, and restrict access to vulnerable devices. Prioritize patching based on the severity of the vulnerability and the potential impact on the organization.

Recommended defensive actions

  • Apply patches for affected Junos OS versions on EX4100 Series and EX4400 devices.
  • Monitor buffer values using 'show chassis fpc' to detect potential memory leaks.
  • Restrict access to vulnerable devices to prevent exploitation.
  • Review compensating controls for exposed systems while remediation is scheduled and verified.
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The CVE record was published on 2026-07-09T22:17:08.093Z and was last modified on 2026-07-10T15:16:45.163Z. The NVD entry is currently Received. This information is based on the supplied source corpus and may need verification. Users should review the official CVE record and NVD entry for the most current details. Evidence limits suggest that further information may be available but has not been confirmed.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-09T22:17:08.093Z and has not been modified since then. The NVD entry is currently Received.