Juniper Junos OS up to 23.2R2-S6/23.4R2-S7/24.2R2-S3/24.4R2-S3 Packet Forwarding Engine infinite loop

Summaryinfo

A vulnerability was found in Juniper Junos OS up to 23.2R2-S6/23.4R2-S7/24.2R2-S3/24.4R2-S3. It has been classified as critical. Affected by this vulnerability is an unknown functionality of the component Packet Forwarding Engine. The manipulation leads to infinite loop. This vulnerability is listed as CVE-2026-57020. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability was found in Juniper Junos OS up to 23.2R2-S6/23.4R2-S7/24.2R2-S3/24.4R2-S3. It has been rated as critical. This issue affects an unknown code block of the component Packet Forwarding Engine. The manipulation with an unknown input leads to a infinite loop vulnerability. Using CWE to declare the problem leads to CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. Impacted is availability. The summary by CVE is:

An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on QFX10000 Series allows an unauthenticated, adjacent attacker to cause a Denial-of-Service (DoS). On all QFX10000 platforms in an EVPN-VxLAN scenario, if an attacker sends IPv6 multicast traffic and these packets reach the non-IRB interface of a spine switch it floods the packet to other spines and all Ethernet Segment Identifier (ESI) leaf switches. This flooding causes the packet to be forwarded in a endless loop, which can lead to saturation of the involved links and in turn impact to legitimate traffic. This issue affects Junos OS on QFX10000 Series: * all versions before 23.2R2-S7, * 23.4 versions before 23.4R2-S8, * 24.2 versions before 24.2R2-S4, * 24.4 versions before 24.4R2-S4. This issue does not affect Junos version after 24.4 as the QFX10000 Series devices are not supported on newer versions anymore.

The advisory is shared at supportportal.juniper.net. The identification of this vulnerability is CVE-2026-57020 since 06/23/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 07/10/2026). MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 23.2R2-S7, 23.4R2-S8, 24.2R2-S4 or 24.4R2-S4 eliminates this vulnerability.

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Productinfo

Type

• Router Operating System

Vendor

• Juniper

Name

• Junos OS

Version

• 23.2R2-S6
• 23.4R2-S7
• 24.2R2-S3
• 24.4R2-S3

License

• commercial

Website

• Vendor: https://www.juniper.net/

CPE 2.3info

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