title: 2023-08-29 Out-of-Cycle Security Bulletin: Junos OS and Junos OS Evolved: A crafted BGP UPDATE message allows a remote attacker to de-peer (reset) BGP sessions (CVE-2023-4481)
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 certain specific crafted BGP UPDATE messages are received over an established BGP session, one BGP session may be torn down with an UPDATE message error, or the issue may propagate beyond the local system which will remain non-impacted, but may affect one or more remote systems. This issue is exploitable remotely as the crafted UPDATE message can propagate through unaffected systems and intermediate BGP speakers.
Continuous receipt of the crafted BGP UPDATE messages will create a sustained Denial of Service (DoS) condition for impacted devices.
This issue affects eBGP and iBGP, in both IPv4 and IPv6 implementations.  This issue requires a remote attacker to have at least one established BGP session.
problem types: CWE-20 Improper Input Validation
affected:
{
defaultStatus: affected
modules: [BGP, rpd]
product: Junos OS
vendor: Juniper Networks, Inc.
versions:
lessThan: 23.4R1, status: affected, version: 0, versionType: semver
}
{
defaultStatus: affected
modules: [BGP, rpd]
product: Junos OS Evolved
vendor: Juniper Networks, Inc.
versions:
lessThan: 23.4R1-EVO, status: affected, version: 0, versionType: semver
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 7.5
baseSeverity: HIGH
confidentialityImpact: NONE
integrityImpact: NONE
privilegesRequired: NONE
scope: UNCHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
version: 3.1
]
format: CVSS
scenarios: GENERAL
exploits: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
solutions: The following software releases have been updated to resolve this specific issue:
Junos OS: 23.4R1*, and all subsequent releases.
Junos OS Evolved: 23.4R1-EVO*, and all subsequent releases.
*Pending Publication – Please note: Additional releases before 23.4R1 for Junos OS and 23.4R1-EVO for Junos OS Evolved are being worked on at this time. Please monitor PRSearch ongoing, and subscribe to this advisory, to see  additional resolved in releases as they become available or as this advisory is updated.
It is important that customers implement the workaround in addition to taking any updated software as these crafted UPDATE messages may be propagated to other devices even if non-impacted locally, thereby protecting the network by stopping the propagation of these crafted UPDATE messages.
The workaround is to configure BGP error tolerance by way of:
[ protocols bgp bgp-error-tolerance ... ]
Additional details can be found at  https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/bgp-error-messages.h... https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/bgp-error-messages.html
Juniper considers configuring this option to be a Best Common Practice (BCP) as it not only prevents this issue from happening, but protects against similar issues as well.
This issue is being tracked as PR  1709837 https://prsearch.juniper.net/problemreport/PR1709837  which is visible on the Customer Support website.
Note: Juniper SIRT's  policy https://kb.juniper.net/KB16765  is not to evaluate releases which are beyond End of Engineering (EOE) or End of Life (EOL).
workarounds: The workaround is to configure BGP error tolerance by way of:
[ protocols bgp bgp-error-tolerance ... ]
Additional details can be found at  https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/bgp-error-messages.h... https://www.juniper.net/documentation/us/en/software/junos/bgp/topics/topic-map/bgp-error-messages.html
Juniper considers configuring this option to be a Best Common Practice (BCP) as it not only prevents this issue from happening, but protects against similar issues as well.
