CVE-2021-0229Junos OS: Receipt of specific packets could lead to Denial of Service in MQTT Server
- 5.3MediumCVSS base score
- 1.2%Exploitation in 30 daysEPSS · top 31% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
An uncontrolled resource consumption vulnerability in Message Queue Telemetry Transport (MQTT) server of Juniper Networks Junos OS allows an attacker to cause MQTT server to crash and restart leading to a Denial of Service (DoS) by sending a stream of specific packets. A Juniper Extension Toolkit (JET) application designed with a listening port uses the Message Queue Telemetry Transport (MQTT) protocol to connect to a mosquitto broker that is running on Junos OS to subscribe for events. Continued receipt and processing of this packet will create a sustained Denial of Service (DoS) condition. This issue affects Juniper Networks Junos OS: 16.1R1 and later versions prior to 17.3R3-S11; 17.4 versions prior to 17.4R2-S13, 17.4R3-S4; 18.1 versions prior to 18.1R3-S12; 18.2 versions prior to 18.2R2-S8, 18.2R3-S7; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R1-S8, 18.4R2-S7, 18.4R3-S7; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S6, 19.2R3-S2; 19.3 versions prior to 19.3R3-S2; 19.4 versions prior to 19.4R2-S4, 19.4R3-S2; 20.1 versions prior to 20.1R2-S1, 20.1R3; 20.2 versions prior to 20.2R2-S2, 20.2R3; 20.3 versions prior to 20.3R1-S1, 20.3R2. This issue does not affect Juniper Networks Junos OS versions prior to 16.1R1.
Timeline
ID reserved
By juniper
- 6 months later
· 6 months later
Published
- 3 years later
· 3 years later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| juniperCNA (assigner) | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
| NVDNVD · Modified | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
- EPSS (exploitation in 30 days)
- 1.2% · top 31% of all CVEs (15 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.
Affected products
- affected 16.1R1 – < 16.1*
- affected 17.3 – < 17.3R3-S11
- affected 17.4 – < 17.4R2-S13, 17.4R3-S4
- affected 18.1 – < 18.1R3-S12
- affected 18.2 – < 18.2R2-S8, 18.2R3-S7
- affected 18.3 – < 18.3R3-S4
- affected 18.4 – < 18.4R1-S8, 18.4R2-S7, 18.4R3-S7
- affected 19.1 – < 19.1R3-S5
- affected 19.2 – < 19.2R1-S6, 19.2R3-S2
- affected 19.3 – < 19.3R3-S2
- affected 19.4 – < 19.4R2-S4, 19.4R3-S2
- affected 20.1 – < 20.1R2-S1, 20.1R3
- affected 20.2 – < 20.2R2-S2, 20.2R3
- affected 20.3 – < 20.3R1-S1, 20.3R2
What to do
Solution: The following software releases have been updated to resolve this specific issue: Junos OS: 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, 19.1R3-S5, 19.2R1-S6, 19.2R3-S2, 19.3R3-S2, 19.4R2-S4, 19.4R3-S2, 20.1R2-S1, 20.1R3, 20.2R2-S2, 20.2R3, 20.3R1-S1, 20.3R2, 20.4R1, and all subsequent releases.
Workaround: There are no viable workarounds for this issue. To reduce the risk of exploitation utilize common security BCPs to limit the exploitable surface by limiting access to network and device to trusted systems, administrators, networks and hosts.
Exploitation: Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
References
References1
- https://kb.juniper.net/JSA11124 (opens in a new tab)x_refsource_MISCx_transferred
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2021-2848 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2021-0229)Record last updated .