CVE-2023-0026: 2023-06: Out-of-Cycle Security Bulletin: Junos OS and Junos OS Evolved: A BGP session will flap upon receipt of a specific, optional transitive attribute

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-06-21 · updated 2026-06-17
Weakness: CWE-20

Description

An Improper Input Validation vulnerability in the Routing Protocol Daemon (rpd) of Juniper Networks Junos OS and Junos OS Evolved allows an unauthenticated, network-based attacker to cause a Denial of Service (DoS). When a BGP update message is received over an established BGP session, and that message contains a specific, optional transitive attribute, this session will be torn down with an update message error. This issue cannot propagate beyond an affected system as the processing error occurs as soon as the update is received. This issue is exploitable remotely as the respective attribute can propagate through unaffected systems and intermediate AS (if any). Continuous receipt of a BGP update containing this attribute will create a sustained Denial of Service (DoS) condition. Some customers have experienced these BGP session flaps which prompted Juniper SIRT to release this advisory out of cycle before fixed releases are widely available as there is an effective workaround. This issue affects: Juniper Networks Junos OS 15.1R1 and later versions prior to 20.4R3-S8; 21.1 version 21.1R1 and later versions prior to 21.2R3-S6; 21.3 versions prior to 21.3R3-S5; 21.4 versions prior to 21.4R3-S4; 22.1 versions prior to 22.1R3-S4; 22.2 versions prior to 22.2R3-S2; 22.3 versions prior to 22.3R2-S2, 22.3R3-S1; 22.4 versions prior to 22.4R2-S1, 22.4R3; 23.1 versions prior to 23.1R1-S1, 23.1R2. Juniper Networks Junos OS Evolved All versions prior to 20.4R3-S8-EVO; 21.1 version 21.1R1-EVO and later versions prior to 21.2R3-S6-EVO; 21.3 versions prior to 21.3R3-S5-EVO; 21.4 versions prior to 21.4R3-S4-EVO; 22.1 versions prior to 22.1R3-S4-EVO; 22.2 versions prior to 22.2R3-S2-EVO; 22.3 versions prior to 22.3R2-S2-EVO, 22.3R3-S1-EVO; 22.4 versions prior to 22.4R2-S1-EVO, 22.4R3-EVO; 23.1 versions prior to 23.1R1-S1-EVO, 23.1R2-EVO.

Affected products

Juniper Junos OS: from 15.1 before 20.4; 20.4, 20.4-r1, 20.4-r1-s1, 20.4-r2, 20.4-r2-s1, 20.4-r2-s2 (+83) — fixed in 20.4
Juniper Networks Junos OS Evolved: before 20.4; 20.4, 20.4-r1, 20.4-r1-s1, 20.4-r1-s2, 20.4-r2, 20.4-r2-s1 (+79) — fixed in 20.4

How to fix

Upgrade to a fixed version: Juniper Junos OS 20.4; Juniper Networks Junos OS Evolved 20.4. Check the vendor advisory for mitigations.

References

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