CVE-2021-0254Public exploitNetwork attack vector

Unauthenticated code execution via unchecked packet copy

Published Apr 22, 2021 · Updated Sep 16, 2024

Buffer overflow in Juniper Networks Junos OS overlayd allows remote attackers to execute code or interrupt service via crafted UDP packets. The overlayd OAM parser passes the received packet length to memcpy without checking it against a fixed BSS destination buffer. The root service listens on UDP port 4789 by default on MX, ACX, and QFX devices; other platforms require VXLAN, and repeated packets sustain the interruption.

CVSS severity9.8
Critical
EPSS probability2.57%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Juniper Networks Junos OS overlayd allows remote attackers to execute code or interrupt service via crafted UDP packets. The overlayd OAM parser passes the received packet length to memcpy without checking it against a fixed BSS destination buffer. The root service listens on UDP port 4789 by default on MX, ACX, and QFX devices; other platforms require VXLAN, and repeated packets sustain the interruption.

The record

CVE
CVE-2021-0254
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-787, CWE-131, T1190, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.1 <15.1R7-S9
  2. Affected versionversion=17.3 <17.3R3-S11
  3. Affected versionversion=17.4 <17.4R2-S13, 17.4R3-S4
  4. Affected versionversion=18.1 <18.1R3-S12
  5. Affected versionversion=18.2 <18.2R2-S8, 18.2R3-S7
  6. Affected versionversion=18.3 <18.3R3-S4
  7. Affected versionversion=18.4 <18.4R1-S8, 18.4R2-S7, 18.4R3-S7
  8. Affected versionversion=19.1 <19.1R2-S2, 19.1R3-S4
  9. Affected versionversion=19.2 <19.2R1-S6, 19.2R3-S2
  10. Affected versionversion=19.3 <19.3R3-S1
  11. Affected versionversion=19.4 <19.4R2-S4, 19.4R3-S1
  12. Affected versionversion=20.1 <20.1R2-S1, 20.1R3
  13. Affected versionversion=20.2 <20.2R2, 20.2R2-S1, 20.2R3
  14. Affected versionversion=20.3 <20.3R1-S1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=15.1 <15.1R7-S9; version=17.3 <17.3R3-S11; version=17.4 <17.4R2-S13, 17.4R3-S4; version=18.1 <18.1R3-S12; version=18.2 <18.2R2-S8, 18.2R3-S7; version=18.3 <18.3R3-S4; version=18.4 <18.4R1-S8, 18.4R2-S7, 18.4R3-S7; version=19.1 <19.1R2-S2, 19.1R3-S4; version=19.2 <19.2R1-S6, 19.2R3-S2; version=19.3 <19.3R3-S1; version=19.4 <19.4R2-S4, 19.4R3-S1; version=20.1 <20.1R2-S1, 20.1R3; version=20.2 <20.2R2, 20.2R2-S1, 20.2R3; version=20.3 <20.3R1-S1

Published CVSS scores

9.8Juniper Networks, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-131Incorrect Calculation of Buffer Size
T1190Exploit Public-Facing Application
T1498Network Denial of Service

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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