CVE-2021-0269Network attack vector

Sensitive-data exfiltration via HTTP parameter pollution

Published Apr 22, 2021 · Updated Sep 17, 2024

HTTP parameter pollution in J-Web in Juniper Networks Junos OS allows remote attackers to exfiltrate data through a user's session. J-Web improperly accepts reflected client-side HTTP parameters that can supersede hardcoded session parameters, expose variables, and bypass input-validation or web-application-firewall rules. J-Web must be enabled and a user must be authenticated to it; exploitation can redirect that user to malicious services or leak sensitive form data.

CVSS severity8.8
High
EPSS probability0.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP parameter pollution in J-Web in Juniper Networks Junos OS allows remote attackers to exfiltrate data through a user's session. J-Web improperly accepts reflected client-side HTTP parameters that can supersede hardcoded session parameters, expose variables, and bypass input-validation or web-application-firewall rules. J-Web must be enabled and a user must be authenticated to it; exploitation can redirect that user to malicious services or leak sensitive form data.

The record

CVE
CVE-2021-0269
Published
Apr 22, 2021
Updated
Sep 17, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-233
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

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Is a vulnerable build present?

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

  1. Affected versionversion=18.1 <18.1R3-S12
  2. Affected versionversion=18.2 <18.2R3-S6
  3. Affected versionversion=18.3 <18.3R3-S4
  4. Affected versionversion=18.4 <18.4R3-S6
  5. Affected versionversion=19.1 <19.1R3-S4
  6. Affected versionversion=19.2 <19.2R3-S1
  7. Affected versionversion=19.3 <19.3R3-S1
  8. Affected versionversion=19.4 <19.4R2-S2, 19.4R3
  9. Affected versionversion=20.1 <20.1R2
  10. Affected versionversion=20.2 <20.2R2
  11. Affected versionversion=unspecified <17.4R3-S3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=18.1 <18.1R3-S12; version=18.2 <18.2R3-S6; version=18.3 <18.3R3-S4; version=18.4 <18.4R3-S6; version=19.1 <19.1R3-S4; version=19.2 <19.2R3-S1; version=19.3 <19.3R3-S1; version=19.4 <19.4R2-S2, 19.4R3; version=20.1 <20.1R2; version=20.2 <20.2R2; version=unspecified <17.4R3-S3

Published CVSS scores

8.8Juniper NetworksCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
5.1NIST NVDAV:N/AC:H/Au:N/C:P/I:P/A:P

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-233Improper Handling of Parameters

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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