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CVE-2021-31366

21
FAUCET Score

CVE-2021-31366 is an Unchecked Return Value vulnerability in Juniper Networks Junos OS on MX Series devices configured for subscriber management. An adjacent attacker can trigger a Denial of Service (DoS) by sending a specific username to the authd (authentication daemon), impacting authentication, authorization, and accounting (AAA) services. This vulnerability has a CVSS score of 6.5 (Medium), indicating a low attack complexity and no user interaction required, with a high impact on availability. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
>= 15.1, < 15.1R7-S9CPE match
cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
>= 17.3, < 17.3R3-S12CPE match
cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
>= 17.4, < 17.4R3-S5CPE match
cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
>= 18.1, < 18.1R3-S13CPE match
cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*
>= 18.2, < 18.2R3-S8CPE match
cpe:2.3:o:juniper:junos:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.5MEDIUM

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

Attack Vector
ADJACENT_NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
NONE
Availability Impact
HIGH
Exploitability Score
2.8
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.41%
Probability of exploitation in next 30 days
EPSS Percentile
33.2%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0041 is in the 50th percentile among its peer group of 1,802 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

juniperpatch availablevia nvd_reference
View patch

References

kb.juniper.net / JSA11228
PatchVendor Advisory