CVE-2021-31366

Adjacent AAA service crash via crafted PPP username

Published Oct 19, 2021 · Updated Sep 17, 2024

Unchecked return value handling in Junos OS authd on MX Series allows attackers to crash AAA services using a crafted PPP username. The daemon fails to check a return value while processing the supplied username, and the resulting failure terminates authd. Exposure requires subscriber management or BBE; repeated PPP login requests sustain the authentication, authorization, and accounting outage.

CVSS severity6.5
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Unchecked return value handling in Junos OS authd on MX Series allows attackers to crash AAA services using a crafted PPP username. The daemon fails to check a return value while processing the supplied username, and the resulting failure terminates authd. Exposure requires subscriber management or BBE; repeated PPP login requests sustain the authentication, authorization, and accounting outage.

The record

CVE
CVE-2021-31366
Published
Oct 19, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-252, T1499
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 19, 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=15.1 <15.1R7-S9
  2. Affected versionversion=17.3 <17.3R3-S12
  3. Affected versionversion=17.4 <17.4R3-S5
  4. Affected versionversion=18.1 <18.1R3-S13
  5. Affected versionversion=18.2 <18.2R3-S8
  6. Affected versionversion=18.3 <18.3R3-S5
  7. Affected versionversion=18.4 <18.4R3-S9
  8. Affected versionversion=19.1 <19.1R3-S6
  9. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S3
  10. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  11. Affected versionversion=19.4 <19.4R3-S3
  12. Affected versionversion=20.1 <20.1R3
  13. Affected versionversion=20.2 <20.2R3-S1
  14. Affected versionversion=20.3 <20.3R3
  15. Affected versionversion=20.4 <20.4R3
  16. Affected versionversion=21.1 <21.1R2

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=15.1 <15.1R7-S9; version=17.3 <17.3R3-S12; version=17.4 <17.4R3-S5; version=18.1 <18.1R3-S13; version=18.2 <18.2R3-S8; version=18.3 <18.3R3-S5; version=18.4 <18.4R3-S9; version=19.1 <19.1R3-S6; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.4 <19.4R3-S3; version=20.1 <20.1R3; version=20.2 <20.2R3-S1; version=20.3 <20.3R3; version=20.4 <20.4R3; version=21.1 <21.1R2

Published CVSS scores

3.3NIST NVDAV:A/AC:L/Au:N/C:N/I:N/A:P
6.5Juniper Networks, Inc.CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-252Unchecked Return Value
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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