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AUSCERT External Security Bulletin Redistribution
JSA11147 - 2021-04 Security Bulletin: Junos OS: Remote code
execution vulnerability in overlayd service
21 April 2021
AusCERT Security Bulletin Summary
Product: Junos OS
Publisher: Juniper Networks
Operating System: Juniper
Impact/Access: Execute Arbitrary Code/Commands -- Remote/Unauthenticated
Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-0254
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2021-04 Security Bulletin: Junos OS: Remote code execution vulnerability in overlayd service (CVE-2021-0254)
Article ID : JSA11147
Last Updated: 20 Apr 2021
Version : 2.0
This issue affects Junos OS 15.1X49, 15.1, 17.3, 17.4, 18.1, 18.2, 18.3, 18.4,
19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3.
A buffer size validation vulnerability in the overlayd service of Juniper
Networks Junos OS may allow an unauthenticated remote attacker to send
specially crafted packets to the device, triggering a partial Denial of Service
(DoS) condition, or leading to remote code execution (RCE). Continued receipt
and processing of these packets will sustain the partial DoS.
The overlayd daemon handles Overlay OAM packets, such as ping and traceroute,
sent to the overlay. The service runs as root by default and listens for UDP
connections on port 4789. This issue results from improper buffer size
validation, which can lead to a buffer overflow. Unauthenticated attackers can
send specially crafted packets to trigger this vulnerability, resulting in
possible remote code execution.
overlayd runs by default in MX Series, ACX Series, and QFX Series platforms.
The SRX Series does not support VXLAN and is therefore not vulnerable to this
Other platforms are also vulnerable if a Virtual Extensible LAN (VXLAN) overlay
network is configured.
This issue affects Juniper Networks Junos OS:
o 15.1 versions prior to 15.1R7-S9;
o 17.3 versions prior to 17.3R3-S11;
o 17.4 versions prior to 17.4R2-S13, 17.4R3-S4;
o 18.1 versions prior to 18.1R3-S12;
o 18.2 versions prior to 18.2R2-S8, 18.2R3-S7;
o 18.3 versions prior to 18.3R3-S4;
o 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7;
o 19.1 versions prior to 19.1R2-S2, 19.1R3-S4;
o 19.2 versions prior to 19.2R1-S6, 19.2R3-S2;
o 19.3 versions prior to 19.3R3-S1;
o 19.4 versions prior to 19.4R2-S4, 19.4R3-S1;
o 20.1 versions prior to 20.1R2-S1, 20.1R3;
o 20.2 versions prior to 20.2R2, 20.2R2-S1, 20.2R3;
o 20.3 versions prior to 20.3R1-S1.
There is no minimum configuration required to be vulnerable to this issue.
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
This issue was discovered during external security research.
This issue has been assigned CVE-2021-0254 .
The following software releases have been updated to resolve this specific
issue: Junos OS 15.1R7-S9, 17.3R3-S11, 17.4R2-S13, 17.4R3-S4, 18.1R3-S12,
18.2R2-S8, 18.2R3-S7, 18.3R3-S4, 18.4R1-S8, 18.4R2-S7, 18.4R3-S7, 19.1R2-S2,
19.1R3-S4, 19.2R1-S6, 19.2R3-S2, 19.3R3-S1, 19.4R2-S4, 19.4R3-S1, 20.1R2-S1,
20.1R3, 20.2R2, 20.2R2-S1, 20.2R3, 20.3R1-S1, 20.4R1, and all subsequent
This fix has also been proactively committed into other releases that might not
be vulnerable to this issue.
This issue is being tracked as 1548415 .
Two methods exist to mitigate this issue:
1. Limit the exploitable attack surface of critical infrastructure networking
equipment by using access lists or firewall filters to limit access to the
device via UDP only from trusted, administrative networks or hosts.
2. Disable Overlay OAM packet via the configuration command: ' set system
processes overlay-ping-traceroute disable '
Software releases or updates are available for download at https://
2021-04-14: Initial Publication.
2021-04-20: Explicitly state that the SRX Series is not vulnerable.
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common
Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."
Juniper SIRT would like to acknowledge and thank Hoang Thach Nguyen (d4rkn3ss)
of STAR Labs for responsibly reporting this vulnerability.
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