CVE-2021-0275Network attack vector

Session takeover via J-Web cross-site scripting

Published Apr 22, 2021 · Updated Sep 17, 2024

Cross-site scripting in J-Web on Juniper Networks Junos OS allows remote attackers to take over an active user's session. Juniper has not disclosed the vulnerable endpoint, input, or missing output-encoding operation that lets attacker-controlled content execute in J-Web. The victim's session must be active; successful exploitation inherits that user's privileges and grants full device control when the victim is root.

CVSS severity8.8
High
EPSS probability1.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in J-Web on Juniper Networks Junos OS allows remote attackers to take over an active user's session. Juniper has not disclosed the vulnerable endpoint, input, or missing output-encoding operation that lets attacker-controlled content execute in J-Web. The victim's session must be active; successful exploitation inherits that user's privileges and grants full device control when the victim is root.

The record

CVE
CVE-2021-0275
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-79
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=12.3 <12.3R12-S15
  2. Affected versionversion=12.3X48 <12.3X48-D95
  3. Affected versionversion=15.1 <15.1R7-S6
  4. Affected versionversion=15.1X49 <15.1X49-D200
  5. Affected versionversion=16.1 <16.1R7-S7
  6. Affected versionversion=16.2 <16.2R2-S11, 16.2R3
  7. Affected versionversion=17.1 <17.1R2-S11, 17.1R3-S2
  8. Affected versionversion=17.2 <17.2R3-S3
  9. Affected versionversion=17.3 <17.3R2-S5, 17.3R3-S7
  10. Affected versionversion=17.4 <17.4R2-S9, 17.4R3
  11. Affected versionversion=18.1 <18.1R3-S9
  12. Affected versionversion=18.2 <18.2R2-S7, 18.2R3-S3
  13. Affected versionversion=18.3 <18.3R1-S7, 18.3R2-S3, 18.3R3-S1
  14. Affected versionversion=18.4 <18.4R1-S6, 18.4R2-S4, 18.4R3
  15. Affected versionversion=19.1 <19.1R2-S1, 19.1R3
  16. Affected versionversion=19.2 <19.2R1-S3, 19.2R2
  17. Affected versionversion=19.3 <19.3R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=12.3 <12.3R12-S15; version=12.3X48 <12.3X48-D95; version=15.1 <15.1R7-S6; version=15.1X49 <15.1X49-D200; version=16.1 <16.1R7-S7; version=16.2 <16.2R2-S11, 16.2R3; version=17.1 <17.1R2-S11, 17.1R3-S2; version=17.2 <17.2R3-S3; version=17.3 <17.3R2-S5, 17.3R3-S7; version=17.4 <17.4R2-S9, 17.4R3; version=18.1 <18.1R3-S9; version=18.2 <18.2R2-S7, 18.2R3-S3; version=18.3 <18.3R1-S7, 18.3R2-S3, 18.3R3-S1; version=18.4 <18.4R1-S6, 18.4R2-S4, 18.4R3; version=19.1 <19.1R2-S1, 19.1R3; version=19.2 <19.2R1-S3, 19.2R2; version=19.3 <19.3R2

Published CVSS scores

8.8Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

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

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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