CVE-2021-0243

MEDIUMNVD 4.74.7—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.7 under NVD CVSS v3. EPSS exploit probability: 0.1%, top 77% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
4.7
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 4.7Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

Improper Handling of Unexpected Data in the firewall policer of Juniper Networks Junos OS on EX4300 switches allows matching traffic to exceed set policer limits, possibly leading to a limited Denial of Service (DoS) condition. When the firewall policer discard action fails on a Layer 2 port, it will allow traffic to pass even though it exceeds set policer limits. Traffic will not get discarded, and will be forwarded even though a policer discard action is configured. When the issue occurs, traffic is not discarded as desired, which can be observed by comparing the Input bytes with the Output bytes using the following command: user@junos> monitor interface traffic Interface Link Input bytes (bps) Output bytes (bps) ge-0/0/0 Up 37425422 (82616) 37425354 (82616) <<<< egress ge-0/0/1 Up 37425898 (82616) 37425354 (82616) <<<< ingress The expected output, with input and output counters differing, is shown below: Interface Link Input bytes (bps) Output bytes (bps) ge-0/0/0 Up 342420570 (54600) 342422760 (54600) <<<< egress ge-0/0/1 Up 517672120 (84000) 342420570 (54600) <<<< ingress This issue only affects IPv4 policing. IPv6 traffic and firewall policing actions are not affected by this issue. This issue affects Juniper Networks Junos OS on the EX4300: All versions prior to 17.3R3-S10; 17.4 versions prior to 17.4R3-S3; 18.1 versions prior to 18.1R3-S11; 18.2 versions prior to 18.2R3-S6; 18.3 versions prior to 18.3R3-S4; 18.4 versions prior to 18.4R3-S6; 19.1 versions prior to 19.1R3-S3; 19.2 versions prior to 19.2R3-S1; 19.3 versions prior to 19.3R3-S1; 19.4 versions prior to 19.4R3; 20.1 versions prior to 20.1R2; 20.2 versions prior to 20.2R2.

CVSS v3
4.7
EG Score
4.7(medium)
EPSS
30.1%
KEV
Not listed

Published

April 22, 2021

Last Modified

November 21, 2024

References (2)

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 47× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

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Frequently asked(5)

What is CVE-2021-0243?
CVE-2021-0243 is a medium vulnerability published on April 22, 2021. Improper Handling of Unexpected Data in the firewall policer of Juniper Networks Junos OS on EX4300 switches allows matching traffic to exceed set policer limits, possibly leading to a limited Denial of Service (DoS) condition. When the firewall policer discard action fails on a Layer 2 port, it…
When was CVE-2021-0243 disclosed?
CVE-2021-0243 was first published in the National Vulnerability Database on April 22, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-0243 actively exploited?
CVE-2021-0243 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 30.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-0243?
CVE-2021-0243 has a CVSS v3 base score of 4.7 (NVD).
How do I remediate CVE-2021-0243?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-0243, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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