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NVD / CVE Program· CNA juniper

CVE-2021-0247: Junos OS: PTX Series, QFX Series: Due to a race condition input loopback firewall filters applied to interfaces may not operate even when listed in the running

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.55% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. Administrator privileges are required. No user action is required. Special conditions such as timing or configuration are required.
  • According to the record, no fixed version is available yet.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

A Race Condition (Concurrent Execution using Shared Resource with Improper Synchronization) vulnerability in the firewall process (dfwd) of Juniper Networks Junos OS allows an attacker to bypass the firewall rule sets applied to the input loopback filter on any interfaces of a device. This issue is detectable by reviewing the PFE firewall rules, as well as the firewall counters and seeing if they are incrementing or not. For example: show firewall Filter: __default_bpdu_filter__ Filter: FILTER-INET-01 Counters: Name Bytes Packets output-match-inet 0 0 <<<<<< missing firewall packet count This issue affects: Juniper Networks Junos OS 14.1X53 versions prior to 14.1X53-D53 on QFX Series; 14.1 versions 14.1R1 and later versions prior to 15.1 versions prior to 15.1R7-S6 on QFX Series, PTX Series; 15.1X53 versions prior to 15.1X53-D593 on QFX Series; 16.1 versions prior to 16.1R7-S7 on QFX Series, PTX Series; 16.2 versions prior to 16.2R2-S11, 16.2R3 on QFX Series, PTX Series; 17.1 versions prior to 17.1R2-S11, 17.1R3-S2 on QFX Series, PTX Series; 17.2 versions prior to 17.2R1-S9, 17.2R3-S3 on QFX Series, PTX Series; 17.3 versions prior to 17.3R2-S5, 17.3R3-S7 on QFX Series, PTX Series; 17.4 versions prior to 17.4R2-S9, 17.4R3 on QFX Series, PTX Series; 18.1 versions prior to 18.1R3-S9 on QFX Series, PTX Series; 18.2 versions prior to 18.2R2-S6, 18.2R3-S3 on QFX Series, PTX Series; 18.3 versions prior to 18.3R1-S7, 18.3R2-S3, 18.3R3-S1 on QFX Series, PTX Series; 18.4 versions prior to 18.4R1-S5, 18.4R2-S3, 18.4R2-S7, 18.4R3 on QFX Series, PTX Series; 19.1 versions prior to 19.1R1-S4, 19.1R2-S1, 19.1R3 on QFX Series, PTX Series; 19.2 versions prior to 19.2R1-S3, 19.2R2 on QFX Series, PTX Series.

MediumCVSS 5.5 · v3.1—No exploit No fix recorded
Published
Apr 22, 2021
Updated
Jun 16, 2026
EPSS
0.5% · 46th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.5%

CNA vs NVD score

NVD
5.5
CNA · juniper
5.1
0.4 point gap

CVSS:3.1/AV:N/AC:H/PR:H/UI:R/S:C/C:L/I:L/A:L

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-0247

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
juniperjunos
juniperqfx10002
juniperqfx10008
juniperqfx10016
juniperqfx5100
juniperqfx5110
juniperqfx5120
juniperqfx5130
juniperqfx5200
juniperqfx5210
juniperqfx5220
juniperptx1000

and 8 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • juniper junos14.1
  • juniper junos14.1x53
  • juniper junos14.2
  • juniper junos15.1
  • juniper junos15.1x53
  • juniper junos16.1
  • juniper junos16.2
  • juniper junos17.1
  • juniper junos17.2
  • juniper junos17.3
  • juniper junos17.4
  • juniper junos18.1
  • juniper junos18.2
  • juniper junos18.3
  • juniper junos18.4
  • juniper junos19.1
  • juniper junos19.2

Versions reported by the vendor

Affected version ranges reported by the assigning authority (juniper). Independent of NVD's CPE analysis and usually ahead of it.

  • Juniper Networks Junos OS

    • 14.1X53 and later · before 14.1X53-D53affected
    • 15.1X53 and later · before 15.1X53-D593affected
    • 14.1R1 and later · before 14.1*affected
    • 15.1 and later · before 15.1R7-S6affected
    • 16.1 and later · before 16.1R7-S7affected
    • 16.2 and later · before 16.2R2-S11, 16.2R3affected
    • 17.1 and later · before 17.1R2-S11, 17.1R3-S2affected
    • 17.2 and later · before 17.2R1-S9, 17.2R3-S3affected
    • 17.3 and later · before 17.3R2-S5, 17.3R3-S7affected
    • 17.4 and later · before 17.4R2-S9, 17.4R3affected

Same product

juniper: all records

Other highest-scoring records for the same primary product.

  • CVE-2023-36845Junos OS: EX and SRX Series: A PHP vulnerability in J-Web allows an unauthenticated to control an important environment variableKEV
    98Now
  • CVE-2023-36846Junos OS: SRX Series: A vulnerability in J-Web allows an unauthenticated attacker to upload arbitrary filesKEV
    79This week
  • CVE-2023-36844Junos OS: EX Series: A PHP vulnerability in J-Web allows an unauthenticated attacker to control important environment variablesKEV
    78This week

Published before and after this one in the same product

  • ← EarlierCVE-2021-0245Apr 22, 2021 · Junos OS: Junos Fusion: Hard-coded credentials on satellite devices allows a locally authenticated attacker to elevate their privileges.
    31Monitor
  • ← EarlierCVE-2021-0246Apr 22, 2021 · Junos OS: SRX1500, SRX4100, SRX4200, SRX4600, SRX5000 Series with SPC2/SPC3: In a multi-tenant environment, a tenant host administrator may be able to jailbreak
    29Monitor
  • Later →CVE-2021-0248Apr 22, 2021 · NFX Series: Hard-coded credentials allow an attacker to take control of any instance through administrative interfaces.
    40Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • Administrator privileges are required.
  • No user action is required.
  • Special conditions such as timing or configuration are required.

If successful

Confidentiality
low · data can be read
Integrity
low · data or configuration can be modified
Availability
low · the service can be disrupted

Impact can extend beyond the vulnerable component (scope changes).

Attack vector
Network
Attack complexity
High
Privileges required
High
User interaction
None
Scope
Changed
Confidentiality impact
Low
Integrity impact
Low
Availability impact
Low

Weakness class (CWE)

CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CVSS vector

CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:L/I:L/A:L

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records