NVD / CVE Program· CNA juniper

CVE-2021-31386: Junos OS: When using J-Web with HTTP an attacker may retrieve encryption keys via Person-in-the-Middle attacks.

Noroxi assessment

Priority: Monitor (action score 23/100)

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: 0.71% (FIRST EPSS); higher than 53.3% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is 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.

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 Protection Mechanism Failure vulnerability in the J-Web HTTP service of Juniper Networks Junos OS allows a remote unauthenticated attacker to perform Person-in-the-Middle (PitM) attacks against the device. This issue affects: Juniper Networks Junos OS 12.3 versions prior to 12.3R12-S20; 15.1 versions prior to 15.1R7-S11; 18.3 versions prior to 18.3R3-S6; 18.4 versions prior to 18.4R3-S10; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R3-S4; 19.3 versions prior to 19.3R3-S4; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R3-S2; 20.2 versions prior to 20.2R3-S3; 20.3 versions prior to 20.3R3-S1; 20.4 versions prior to 20.4R3; 21.1 versions prior to 21.1R3; 21.2 versions prior to 21.2R2.

MediumCVSS 5.9 · v3.1—No exploit No fix recorded

Pre-auth

Published: Oct 19, 2021
Updated: Jun 16, 2026
EPSS: 0.7% · 53th percentile
CWE: CWE-300

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 23 / 40 · 5.9 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.7%

CNA vs NVD score

NVD: 5.9
CNA · juniper: 5.3; 0.6 point gap

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

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.

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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.

Vendor	Product	CPE
juniper	junos	cpe:2.3:o:juniper:junos

Affected versions

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

juniper junos12.3
juniper junos15.1
juniper junos18.3
juniper junos18.4
juniper junos19.1
juniper junos19.2
juniper junos19.3
juniper junos19.4
juniper junos20.1
juniper junos20.2
juniper junos20.3
juniper junos20.4
juniper junos21.1
juniper junos21.2

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
- 12.3 and later · before 12.3R12-S20affected
- 15.1 and later · before 15.1R7-S11affected
- 18.3 and later · before 18.3R3-S6affected
- 18.4 and later · before 18.4R3-S10affected
- 19.1 and later · before 19.1R3-S7affected
- 19.2 and later · before 19.2R3-S4affected
- 19.3 and later · before 19.3R3-S4affected
- 19.4 and later · before 19.4R3-S6affected
- 20.1 and later · before 20.1R3-S2affected
- 20.2 and later · before 20.2R3-S3affected

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-2021-31384Oct 19, 2021 · Junos OS: SRX Series: Under a specific device configuration an attacker can access the devices J-Web management services from any interface, regardless of secur
40Plan
← EarlierCVE-2021-31385Oct 19, 2021 · Junos OS: J-Web: A path traversal vulnerability allows an authenticated attacker to elevate their privileges to root
35Monitor
Later →CVE-2022-22153Jan 18, 2022 · SRX Series and MX Series with SPC3: A high percentage of fragments might lead to high latency or packet drops
30Monitor

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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

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.

Andy ColesMicrosoft MSRC Vulnerabilities and Mitigations Team

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).

Technical details

Attack conditions

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

If successful

Confidentiality: high · data can be read
Integrity: none
Availability: none

Attack vector: Network
Attack complexity: High
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: None
Availability impact: None

Weakness class (CWE)

CWE-300 · Channel Accessible by Non-Endpoint

CVSS vector

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

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.

Attack patterns (CAPEC)

ATT&CK techniques

Change log

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

References

kb.juniper.net/JSA11254

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

All records