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AUSCERT External Security Bulletin Redistribution
JSA11149 - 2021-04 Security Bulletin: Junos OS: Kernel panic upon receipt
of specific TCPv6 packet on management interface
16 April 2021
AusCERT Security Bulletin Summary
Product: Junos OS
Publisher: Juniper Networks
Operating System: Juniper
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-0258
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2021-04 Security Bulletin: Junos OS: Kernel panic upon receipt of specific TCPv6
packet on management interface (CVE-2021-0258)
Article ID : JSA11149
Last Updated: 15 Apr 2021
Version : 2.0
This issue affects Junos OS 17.2, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1,
19.2, 19.3, 19.4.
A vulnerability in the forwarding of transit TCPv6 packets received on the
Ethernet management interface of Juniper Networks Junos OS allows an attacker
to trigger a kernel panic, leading to a Denial of Service (DoS). Continued
receipt and processing of these transit packets will create a sustained Denial
of Service (DoS) condition. This issue only occurs when TCPv6 packets are
routed through the management interface. Other transit traffic, and traffic
destined to the management interface, are unaffected by this vulnerability.
This issue was introduced as part of a TCP Parallelization feature added in
Junos OS 17.2, and affects systems with concurrent network stack enabled. This
feature is enabled by default, but can be disabled (see WORKAROUND section
This issue affects Juniper Networks Junos OS:
o 17.2R1-S7, 17.2R1-S8, 17.2R3 and later versions prior to 17.2R3-S4;
o 17.3 versions prior to 17.3R3-S9;
o 17.4 versions prior to 17.4R2-S11, 17.4R3-S2;
o 18.1 versions prior to 18.1R3-S11;
o 18.2 versions prior to 18.2R3-S5;
o 18.3 versions prior to 18.3R2-S4, 18.3R3-S3;
o 18.4 versions prior to 18.4R2-S5, 18.4R3-S4;
o 19.1 versions prior to 19.1R2-S2, 19.1R3;
o 19.2 versions prior to 19.2R1-S5, 19.2R2;
o 19.3 versions prior to 19.3R2-S4, 19.3R3;
o 19.4 versions prior to 19.4R1-S3, 19.4R2.
This issue does not affect Juniper Networks Junos OS 17.2 versions prior to
17.2R1-S7, or any version of 17.2R2.
Any configuration with IPv6 enabled on the management interface is vulnerable
to this issue. For example:
[interfaces fxp0 unit 0 family inet6]
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
This issue was found during internal product security testing or research.
This issue has been assigned CVE-2021-0258 .
The following software releases have been updated to resolve this specific
issue: Junos OS 17.2R3-S4, 17.3R3-S9, 17.4R2-S11, 17.4R3-S2, 18.1R3-S11,
18.2R3-S5, 18.3R2-S4, 18.3R3-S3, 18.4R2-S5, 18.4R3-S4, 19.1R2-S2, 19.1R3,
19.2R1-S5, 19.2R2, 19.3R2-S4, 19.3R3, 19.4R1-S3, 19.4R2, 20.1R1, and all
This issue is being tracked as 1477824 .
Disable TCP Parallelization:
set system kernel-smp-features disable-concurrent-network-stack
Software releases or updates are available for download at https://
2021-04-14: Initial Publication.
2021-04-15: Further clarification of Junos OS 17.2 affected releases.
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common
Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."
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