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2021-10 Security Bulletin: Junos OS: When using J-Web with HTTP an attacker may retrieve encryption keys via Person-in-the-Middle attacks. (CVE-2021-31386)



Article ID: JSA11254 SECURITY_ADVISORIES Last Updated: 13 Oct 2021Version: 2.0
Product Affected:
This issue affects Junos OS 12.3, 15.1, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, 20.3, 20.4, 21.1, 21.2.

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.

The device must have J-Web's HTTP services enabled to be susceptible to this issue:

[system services web-management http]

Juniper SIRT is not aware of any malicious exploitation of this vulnerability.

This issue was discovered during external security research.

This issue has been assigned CVE-2021-31386.


The following software releases have been updated to resolve this specific issue: 12.3R12-S20, 15.1R7-S11, 18.3R3-S6, 18.4R3-S10, 19.1R3-S7, 19.2R3-S4, 19.3R3-S4, 19.4R3-S6, 20.1R3-S2, 20.2R3-S3, 20.3R3-S1, 20.4R3, 21.1R3, 21.2R2, 21.3R1, and all subsequent releases.

Note: Use of HTTP must also be discontinued.

This issue is being tracked as 1603199.


Discontinue the use of HTTP, instead use HTTPS when using J-Web.

[system services web-management https]
Software releases or updates are available for download at
Modification History:
2021-10-13: Initial Publication.
CVSS Score:
5.3 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N)
Severity Level:
Severity Assessment:
Information for how Juniper Networks uses CVSS can be found at KB 16446 "Common Vulnerability Scoring System (CVSS) and Juniper's Security Advisories."
Andy Coles of Microsoft MSRC Vulnerabilities and Mitigations Team

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