CVE-2021-31355

Name: CVE-2021-31355
Creator: NVD / NIST
Published: 2021-10-19T19:15:08.837+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.4/10EPSS 0.78%

Last modified Jun 17, 2026

CVE-2021-31355 is a medium-severity vulnerability rated 5.4/10 on the CVSS scale. A persistent cross-site scripting (XSS) vulnerability in the captive portal graphical user interface of Juniper Networks Junos OS may allow a remote authenticated user to inject web script or HTML and steal sensitive data and credentials from a web administration session, possibly tricking a follow-on administrative user to perform administrative actions on the device. This issue affects Juniper Networks Junos OS: All versions, including the following supported releases: 12.3X48 versions prior to 12.3X48-D105; 15.1X49 versions prior to 15.1X49-D220; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R3-S4; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R1-S1, 20.2R2; 20.3 versions prior to 20.3R2; 20.4 versions prior to 20.4R2; 21.1 versions prior to 21.1R2.. EPSS estimates a 0.78% chance of exploitation in the next 30 days.

Description

A persistent cross-site scripting (XSS) vulnerability in the captive portal graphical user interface of Juniper Networks Junos OS may allow a remote authenticated user to inject web script or HTML and steal sensitive data and credentials from a web administration session, possibly tricking a follow-on administrative user to perform administrative actions on the device. This issue affects Juniper Networks Junos OS: All versions, including the following supported releases: 12.3X48 versions prior to 12.3X48-D105; 15.1X49 versions prior to 15.1X49-D220; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S9; 19.1 versions prior to 19.1R3-S7; 19.2 versions prior to 19.2R3-S3; 19.3 versions prior to 19.3R3-S4; 19.4 versions prior to 19.4R3-S6; 20.1 versions prior to 20.1R3; 20.2 versions prior to 20.2R1-S1, 20.2R2; 20.3 versions prior to 20.3R2; 20.4 versions prior to 20.4R2; 21.1 versions prior to 21.1R2.

Metrics

CVSS 3.1

5.4/10

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

EPSS Probability

0.78%

51.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions	Update
Juniper	Junos	12.3x48	—
Juniper	Junos	15.1x49	—
Juniper	Junos	18.3	—
Juniper	Junos	18.4	—
Juniper	Junos	19.1	—
Juniper	Junos	19.2	—
Juniper	Junos	19.3	—
Juniper	Junos	19.4	R1
Juniper	Junos	20.1	R1
Juniper	Junos	20.2	R1
Juniper	Junos	20.3	R1
Juniper	Junos	20.4	R1
Juniper	Junos	21.1	R1

References

https://kb.juniper.net/JSA11220Patch, Vendor Advisory
https://kb.juniper.net/JSA11220Patch, Vendor Advisory

Timeline

Published: Oct 19, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-31355?

How severe is CVE-2021-31355?

CVE-2021-31355 has a CVSS score of 5.4/10 (MEDIUM severity). The EPSS model estimates a 0.78% probability of exploitation in the next 30 days.

How do I fix CVE-2021-31355?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-31355?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST