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CVE-2021-31355

Junos OS: Stored Cross-Site Scripting (XSS) vulnerability in captive portal

High8.0EPSS 0.81%
Published
Updated
Reserved
Assigned by
juniper

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.

Timeline

  1. ID reserved

    By juniper

  2. · 6 months later

    Published

  3. · 3 years later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2021-31355, by who scored it
Scored byCVSSScoreVector
juniperCNA (assigner)3.1High8.0CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
NVDNVD · Modified3.1Medium5.4CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
EPSS (exploitation in 30 days)
0.81% · top 43% of all CVEs (7 Nov 2026)
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.0.

Weakness

Affected products

  • Juniper Networks · Junos OS

    • affected 12.3X48 – < 12.3X48-D105
    • affected 15.1X49 – < 15.1X49-D220
    • affected 18.3 – < 18.3R3-S5
    • affected 18.4 – < 18.4R3-S9
    • affected 19.1 – < 19.1R3-S7
    • affected 19.2 – < 19.2R3-S3
    • affected 19.3 – < 19.3R3-S4
    • affected 19.4 – < 19.4R3-S6
    • affected 20.1 – < 20.1R3
    • affected 20.2 – < 20.2R1-S1, 20.2R2
    • affected 20.3 – < 20.3R2
    • affected 20.4 – < 20.4R2
    • affected 21.1 – < 21.1R2

What to do

Solution: The following software releases have been updated to resolve this specific issue: Junos OS 12.3X48-D105, 15.1X49-D220, 18.3R3-S5, 18.4R3-S9, 19.1R3-S7, 19.2R3-S3, 19.3R3-S4, 19.4R3-S6, 20.1R3, 20.2R1-S1, 20.2R2, 20.3R2, 20.4R2, 21.1R2, 21.2R1 and all subsequent releases. Additionally, after performing an upgrade to a resolved release, additional steps must be taken to ensure that all stored malicious scripts are removed from the configuration.

Workaround: There are no viable workarounds for this issue.

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

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .