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JunosOperating system · Juniper

CVE-2021-31373

MEDIUM · 5.4 CVSS v3.1 Published 2021-10-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
58/100
Remediation priority · Elevated
Remotely reachable

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A persistent Cross-Site Scripting (XSS) vulnerability in Juniper Networks Junos OS on SRX Series, J-Web interface may allow a remote authenticated user to inject persistent and malicious scripts. An attacker can exploit this vulnerability to steal sensitive data and credentials from a web administration session, or hijack another user's active session to perform administrative actions. This issue affects: Juniper Networks Junos OS on SRX Series: 18.2 versions prior to 18.2R3-S8; 18.3 versions prior to 18.3R3-S5; 18.4 versions prior to 18.4R3-S8; 19.1 versions prior to 19.1R3-S5; 19.2 versions prior to 19.2R1-S7, 19.2R3-S3; 19.3 versions prior to 19.3R2-S6, 19.3R3-S3; 19.4 versions prior to 19.4R1-S4, 19.4R2-S4, 19.4R3-S3; 20.1 versions prior to 20.1R2-S2, 20.1R3; 20.2 versions prior to 20.2R3-S1; 20.3 versions prior to 20.3R2-S1, 20.3R3.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A persistent (stored) Cross-Site Scripting vulnerability exists in the J-Web interface of Juniper Networks Junos OS on SRX Series devices. An authenticated attacker can inject malicious JavaScript scripts that get stored on the device and executed in the browsers of other users accessing the J-Web interface, enabling session hijacking and credential theft.

MitigationApply the appropriate Junos OS patch as specified in Juniper's advisory for the specific version running on the SRX device, or upgrade to a fixed release (18.2R3-S8 or later, 18.3R3-S5 or later, etc.).

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1= 20.2= 20.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm device is an SRX Series platform
    Run 'show chassis hardware' or 'show system information' and verify the model field shows an SRX device (e.g., SRX340, SRX550, etc.)
    Affected if The device model is not an SRX Series device - this vulnerability only affects SRX appliances
  2. Identify the installed Junos OS version
    Run 'show version' and note the Junos OS version number (e.g., 18.2R3.5, 20.3R1.2)
    Affected if The version matches any of the affected releases: 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1, 20.2, or 20.3 (any build within these release trains)
  3. Verify J-Web interface is enabled
    Run 'show configuration system services web-management' and check for 'https' or 'http' configuration under web-management
    Affected if J-Web (web-management) is actively enabled and accessible - the XSS only executes when users access the J-Web interface
  4. Inspect J-Web configuration for injected scripts
    Run 'show configuration | display set | match jweb' or review the saved configuration for any unexpected script tags, JavaScript declarations, or suspicious URL parameters within J-Web related settings
    Affected if Unexpected script content, encoded payloads, or foreign characters appear within J-Web or system services configuration blocks

The device is affected if it is an SRX Series running a Junos OS version in the 18.2 through 20.3 range AND the J-Web interface is enabled, allowing stored malicious scripts to execute in other users' browsers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the appropriate Junos OS patch as specified in Juniper's advisory for the specific version running on the SRX device, or upgrade to a fixed release (18.2R3-S8 or later, 18.3R3-S5 or later, etc.).

Recommended fix High confidence

Upgrade to 18.2R3-S8 or later (18.2.x), 18.3R3-S5 or later (18.3.x), 18.4R3-S8 or later (18.4.x), or 19.1R3-S5 or later (19.1.x) depending on current branch

  1. 1. Identify the current Junos OS version running on the SRX Series device using 'show version' command.
  2. 2. Based on the current version, plan upgrade to the appropriate fixed release: For 18.2.x upgrade to 18.2R3-S8 or later; For 18.3.x upgrade to 18.3R3-S5 or later; For 18.4.x upgrade to 18.4R3-S8 or later; For 19.1.x upgrade to 19.1R3-S5 or later.
  3. 3. Download the recommended Junos OS software package from the Juniper Networks download portal (https://www.juniper.net/customers/csc/software/).
  4. 4. Upload the software package to the device using 'file copy' or via the web interface.
  5. 5. Install the new software package using 'request system software add <package-name> reboot' command.
  6. 6. After reboot, verify the new version is installed using 'show version' and confirm the vulnerability is remediated.
  7. 7. Clear browser cache and test J-Web interface functionality.
Caveat Standard Junos upgrade may cause brief service disruption; ensure valid configuration backup before upgrade; some legacy features may be deprecated in newer releases

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-31373 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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