CVE-2021-0261Network attack vector

Unauthenticated service interruption via request flood

Published Apr 22, 2021 · Updated Sep 16, 2024

Denial of service in Junos OS HTTP/HTTPS services allows remote attackers to interrupt J-Web and related services via specific request floods. The vulnerable HTTP/HTTPS service mishandles a high number of specially formed requests, exhausting service resources and leaving web-based functions unavailable for an extended period. Exploitation requires no authentication but does require network reachability to an enabled web-management, Web Authentication, Dynamic-VPN, firewall-authentication redirect, or Captive Portal service; the documented impact is service interruption without reported data disclosure or configuration change.

CVSS severity7.5
High
EPSS probability1.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Junos OS HTTP/HTTPS services allows remote attackers to interrupt J-Web and related services via specific request floods. The vulnerable HTTP/HTTPS service mishandles a high number of specially formed requests, exhausting service resources and leaving web-based functions unavailable for an extended period. Exploitation requires no authentication but does require network reachability to an enabled web-management, Web Authentication, Dynamic-VPN, firewall-authentication redirect, or Captive Portal service; the documented impact is service interruption without reported data disclosure or configuration change.

The record

CVE
CVE-2021-0261
Published
Apr 22, 2021
Updated
Sep 16, 2024
Vendor
Juniper Networks
Product
Junos OS
Classifications
CWE-125, CWE-770, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 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=12.3 <12.3R12-S17
  2. Affected versionversion=12.3X48 <12.3X48-D105
  3. Affected versionversion=15.1 <15.1R7-S8
  4. Affected versionversion=15.1X49 <15.1X49-D230
  5. Affected versionversion=16.1 <16.1R7-S8
  6. Affected versionversion=17.4 <17.4R2-S12, 17.4R3-S3
  7. Affected versionversion=18.1 <18.1R3-S11
  8. Affected versionversion=18.2 <18.2R3-S6
  9. Affected versionversion=18.3 <18.3R2-S4, 18.3R3-S3
  10. Affected versionversion=18.4 <18.4R2-S5, 18.4R3-S4
  11. Affected versionversion=19.1 <19.1R2-S2, 19.1R3-S2
  12. Affected versionversion=19.2 <19.2R1-S5, 19.2R3
  13. Affected versionversion=19.3 <19.3R2-S4, 19.3R3
  14. Affected versionversion=19.4 <19.4R1-S3, 19.4R2-S2, 19.4R3
  15. Affected versionversion=20.1 <20.1R1-S3, 20.1R2
  16. Affected versionversion=20.2 <20.2R1-S1, 20.2R2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Juniper Networks · Junos OSversion=12.3 <12.3R12-S17; version=12.3X48 <12.3X48-D105; version=15.1 <15.1R7-S8; version=15.1X49 <15.1X49-D230; version=16.1 <16.1R7-S8; version=17.4 <17.4R2-S12, 17.4R3-S3; version=18.1 <18.1R3-S11; version=18.2 <18.2R3-S6; version=18.3 <18.3R2-S4, 18.3R3-S3; version=18.4 <18.4R2-S5, 18.4R3-S4; version=19.1 <19.1R2-S2, 19.1R3-S2; version=19.2 <19.2R1-S5, 19.2R3; version=19.3 <19.3R2-S4, 19.3R3; version=19.4 <19.4R1-S3, 19.4R2-S2, 19.4R3; version=20.1 <20.1R1-S3, 20.1R2; version=20.2 <20.2R1-S1, 20.2R2

Published CVSS scores

7.5NVD/Juniper CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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.

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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Endpoint Denial of Service: Application Exhaustion

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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