CVE-2021-31373Network attack vector

Session hijacking via persistently stored J-Web scripts

Published Oct 19, 2021 · Updated Sep 16, 2024

Persistent XSS in Juniper Networks Junos OS on SRX Series allows remote authenticated users to hijack J-Web administrator sessions. The J-Web interface persistently stores insufficiently validated script content and later renders it in another administrator's browser. Exploitation requires authenticated J-Web access and interaction by another administrator, exposing credentials and permitting actions through the victim's active session.

CVSS severity8.0
High
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Persistent XSS in Juniper Networks Junos OS on SRX Series allows remote authenticated users to hijack J-Web administrator sessions. The J-Web interface persistently stores insufficiently validated script content and later renders it in another administrator's browser. Exploitation requires authenticated J-Web access and interaction by another administrator, exposing credentials and permitting actions through the victim's active session.

The record

CVE
CVE-2021-31373
Published
Oct 19, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-79, CWE-20
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 19, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=18.2 <18.2R3-S8
  2. Affected versionversion=18.3 <18.3R3-S5
  3. Affected versionversion=18.4 <18.4R3-S8
  4. Affected versionversion=19.1 <19.1R3-S5
  5. Affected versionversion=19.2 <19.2R1-S7, 19.2R3-S3
  6. Affected versionversion=19.3 <19.3R2-S6, 19.3R3-S3
  7. Affected versionversion=19.4 <19.4R1-S4, 19.4R2-S4, 19.4R3-S3
  8. Affected versionversion=20.1 <20.1R2-S2, 20.1R3
  9. Affected versionversion=20.2 <20.2R3-S1
  10. Affected versionversion=20.3 <20.3R2-S1, 20.3R3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Juniper Networks · Junos OSversion=18.2 <18.2R3-S8; version=18.3 <18.3R3-S5; version=18.4 <18.4R3-S8; version=19.1 <19.1R3-S5; version=19.2 <19.2R1-S7, 19.2R3-S3; version=19.3 <19.3R2-S6, 19.3R3-S3; version=19.4 <19.4R1-S4, 19.4R2-S4, 19.4R3-S3; version=20.1 <20.1R2-S2, 20.1R3; version=20.2 <20.2R3-S1; version=20.3 <20.3R2-S1, 20.3R3

Published CVSS scores

5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
8.0Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-20Improper Input Validation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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