CVE-2021-0273Network attack vector

Service interruption via Trio microcode infinite loop

Published Apr 22, 2021 · Updated Sep 17, 2024

Infinite-loop denial of service in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to interrupt LT-LT interfaces. Implicit filter terms in Trio PFE UCODE use always-incorrect control flow, so a packet destined to an affected interface loops without reaching an exit. Only specified Trio line cards on LT-LT interfaces are exposed; continued packet processing sustains the interruption until one side is disabled.

CVSS severity5.3
Medium
EPSS probability1.00%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite-loop denial of service in Juniper Networks Junos OS and Junos OS Evolved allows remote attackers to interrupt LT-LT interfaces. Implicit filter terms in Trio PFE UCODE use always-incorrect control flow, so a packet destined to an affected interface loops without reaching an exit. Only specified Trio line cards on LT-LT interfaces are exposed; continued packet processing sustains the interruption until one side is disabled.

The record

CVE
CVE-2021-0273
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS Evolved
Classifications
CWE-670, CWE-835, T1498
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=19.4 <19.4R2-EVO

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OS Evolvedversion=19.4 <19.4R2-EVO
Juniper Networks · Junos OSversion=15.1F6 <15.1*; version=16.1R1 <16.1* changes=[{"at":"16.1R7-S8","status":"unaffected"}]; version=17.1 <17.1R2-S12; version=17.2 <17.2R3-S4; version=17.3 <17.3R3-S8; version=17.4 <17.4R2-S10, 17.4R3-S2; version=18.1 <18.1R3-S10; version=18.2 <18.2R2-S7, 18.2R3-S3; version=18.3 <18.3R1-S7, 18.3R3-S2; version=18.4 <18.4R1-S7, 18.4R2-S4, 18.4R3-S2; version=19.1 <19.1R1-S5, 19.1R2-S1, 19.1R3; version=19.2 <19.2R1-S4, 19.2R2; version=19.3 <19.3R2-S3, 19.3R3; version=19.4 <19.4R1-S1, 19.4R2

Published CVSS scores

5.3Juniper Networks, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/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 exploitUnconfirmed

Weakness, pattern, technique

CWE-670Always-Incorrect Control Flow Implementation
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1498Network Denial of Service

Public exploit references

No public exploit references are available in this record.

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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