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Full vulnerability report · 2026
CVE-2026-21901High confidence

Junos OS and Junos OS Evolved: Configuration of a specific SSH option results in mgd crash

Juniper Networks · Junos OS

Official source article: GitHub GHSA-G4F7-W2RC-HPJ6 ↗. Check the applicable product and release in the original source.

6.7MediumCVSS 4.0
Recommended action
Within 7 days

Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • A structured source references public exploit or proof-of-concept material.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 0.17% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Increase monitoring for the attack path and post-exploitation behaviour described in the report.

Verification

  1. Confirm that the asset runs Juniper Networks Junos OS and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-42697

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

Medium technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

A NULL Pointer Dereference vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a local, high-privileged attacker setting or deactivating a specific SSH configuration parameter to create a Denial of Service (DoS). A local high-privileged user configuring or deactivating a specific 'system services ssh' configuration parameter can exploit a null pointer dereference in one of the functions used by SSH. The function attempts to dereference a null pointer when accessing certain configuration data, resulting in an mgd process crash and restart. Continued execution of these configuration commands will create a sustained Denial of Service (DoS) condition. This issue affects: Junos OS: * from 22.3 before 22.3R3-S5; * from 22.4 before 22.4R3-S10; * from 23.2 before 23.2R2-S7; * from 23.4 before 23.4R2-S8. This issue does not affect Junos OS before 22.3R1. Junos OS Evolved: * from 22.3R1-EVO before 23.2R2-S7-EVO; * from 23.4 before 23.4R2-S8-EVO. This issue does not affect Junos OS Evolved before 22.3R1-EVO.

What

A NULL Pointer Dereference vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a local, high-privileged attacker setting or deactivating a specific SSH configuration parameter to create a Denial of Service (DoS). A local high-privileged user configuring or deactivating a specific 'system services ssh' configuration parameter can exploit a null pointer dereference in one of the functions used by SSH. The function attempts to dereference a null pointer when accessing certain configuration data, resulting in an mgd process crash and restart. Continued execution of these configuration commands will create a sustained Denial of Service (DoS) condition. This issue affects: Junos OS: * from 22.3 before 22.3R3-S5; * from 22.4 before 22.4R3-S10; * from 23.2 before 23.2R2-S7; * from 23.4 before 23.4R2-S8. This issue does not affect Junos OS before 22.3R1. Junos OS Evolved: * from 22.3R1-EVO before 23.2R2-S7-EVO; * from 23.4 before 23.4R2-S8-EVO. This issue does not affect Junos OS Evolved before 22.3R1-EVO.

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through local access may attempt exploitation with elevated privileges. If successful, the issue may disrupt the affected service.

What

A NULL Pointer Dereference vulnerability in the management daemon (mgd) of Juniper Networks Junos OS and Junos OS Evolved allows a local, high-privileged attacker setting or deactivating a specific SSH configuration parameter to create a Denial of Service (DoS). A local high-privileged user configuring or deactivating a specific 'system services ssh' configuration parameter can exploit a null pointer dereference in one of the functions used by SSH. The function attempts to dereference a null pointer when accessing certain configuration data, resulting in an mgd process crash and restart. Continued execution of these configuration commands will create a sustained Denial of Service (DoS) condition. This issue affects: Junos OS: * from 22.3 before 22.3R3-S5; * from 22.4 before 22.4R3-S10; * from 23.2 before 23.2R2-S7; * from 23.4 before 23.4R2-S8. This issue does not affect Junos OS before 22.3R1. Junos OS Evolved: * from 22.3R1-EVO before 23.2R2-S7-EVO; * from 23.4 before 23.4R2-S8-EVO. This issue does not affect Junos OS Evolved before 22.3R1-EVO.

Why

The product dereferences a pointer that it expects to be valid but is NULL.

How

An attacker operating through local access may attempt exploitation with elevated privileges. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
Reference recorded

A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.

Likely attack path
local access → NULL Pointer Dereference → disrupt the affected service
Attack surface
Local
Privileges required
High: elevated access is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Not a CVSS 4.0 base metric
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-476 ↗

CWE-476: NULL Pointer Dereference. The product dereferences a pointer that it expects to be valid but is NULL.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:4.0/AV:L/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/AU:Y/R:A/V:D/RE:M/U:Green

Common Vulnerability Scoring System 4.0: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.ATNoneAttack requirements: No additional deployment or execution condition is required.PRHighPrivileges required: The attacker needs elevated or administrative privileges.UINoneUser interaction: No action by another user is required.VCNoneVulnerable-system confidentiality: No direct loss is represented by this metric.VINoneVulnerable-system integrity: No direct loss is represented by this metric.VAHighVulnerable-system availability: A successful attack can cause a major loss.SCNoneSubsequent-system confidentiality: No direct loss is represented by this metric.SINoneSubsequent-system integrity: No direct loss is represented by this metric.SANoneSubsequent-system availability: No direct loss is represented by this metric.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
Denial of serviceCWE-476Public exploit reference
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-2257Juniper JUNOS und JUNOS Evolved: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Juniper JUNOS, JUNOS Evolved, Juniper EX Series, Juniper MX Series, Juniper QFX Series und Juniper SRX Series ausnutzen, um einen Denial of Service Zustand herbeizuführen, um Informationen offenzulegen, um Code auszuführen und um ein undefiniertes Verhalten auszulösen.

Official advisory ↗
CERT-FR · French · CERTFR-2026-AVI-0852Multiples vulnérabilités dans les produits Juniper Networks

ecurity-Bulletin-cRPD-Multiple-vulnerabilities-resolved-in-cRPD-26-2R1 du 08 juillet 2026 Bulletin de sécurité Juniper Networks 2026-07-Security-Bulletin-CTPView-Multiple-vulnerabilities-resolved-in-9-3R2-3-Release du 08 juillet 2026 Bulletin de sécurité Juniper Networks 2026-07-Security-Bulletin-Junos-Space-Multiple-vulnerabilities-resolved-in-26-1R1-Patch-V1-Release du 08 juillet 2026 Bulletin de sécurité Juniper Networks 2026-07-Security-Bulletin-Network-Director-Multiple-vulnerabilities-resolved-in-7-1R3-release du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2020-7450 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-21901 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33794 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33799 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33800 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33801 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33802 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-33803 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-57019 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-57020 du 08 juillet 2026 Bulletin de sécurité Juniper Networks CVE-2026-57021 d

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-030413ジュニパーネットワークスのJunos OS等の複数製品におけるNULL ポインタデリファレンスに関する脆弱性

Juniper NetworksのJunos OSおよびJunos OS Evolvedの管理デーモン(mgd)におけるNULLポインタ参照脆弱性により、ローカルの高権限攻撃者が特定のSSH設定パラメータを設定または無効化することでサービス拒否（DoS）を引き起こす可能性があります。ローカルの高権限ユーザーは特定の「system services ssh」設定パラメータを設定または無効化する際に、SSHで使用される関数の一つにおけるNULLポインタ参照を悪用することが可能です。この関数は特定の設定データにアクセスする際にNULLポインタを参照しようとし、その結果mgdプロセスがクラッシュして再起動します。これらの設定コマンドを継続して実行することで、持続的なサービス拒否（DoS）状態が引き起こされます。この問題は以下のJunos OSのバージョンに影響を及ぼします： * 22.3から22.3R3-S5より前まで、 * 22.4から22.4R3-S10より前まで、 * 23.2から23.2R2-S7より前まで、 * 23.4から23.4R2-S8より前まで。なお、この問題は22.3R1以前のJunos OSには影響しません。Junos OS Evolvedでは以下のバージョンに影響があります： * 22.3R1-EVOから23.2R2-S7-EVOより前まで、 * 23.4から23.4R2-S8-EVOより前まで。22.3R1-EVO以前のJunos OS Evolvedには影響がありません。

Official advisory ↗
NCSC-NL · Dutch · NCSC-2026-0224Kwetsbaarheden verholpen in Juniper Networks Junos OS en Junos OS Evolved

A NULL Pointer Dereference vulnerability in Juniper Networks Junos OS and Junos OS Evolved management daemon allows a local high-privileged attacker to cause a Denial of Service by manipulating a specific SSH configuration parameter, leading to mgd process crashes and restarts.

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 9 Jul 2026 · Last source change 10 Jul 2026, 14:21 UTC · CWE-476 · NULL Pointer Dereference

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-42697
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Vendor guidanceAuthoritative vendor guidance changed: added mitigation: github.com/GHSA-g4f7-w2rc-hpj6; added vendor advisory: supportportal.juniper.net/JSA110072.
    Before
    remediation: github.com/GHSA-g4f7-w2rc-hpj6
    After
    mitigation: github.com/GHSA-g4f7-w2rc-hpj6 · remediation: github.com/GHSA-g4f7-w2rc-hpj6 · vendor advisory: supportportal.juniper.net/JSA110072
    github.com ↗
  2. Public exploit evidencePublic exploit evidence changed from Public exploit reference to Public exploit reference.
    Before
    Public exploit reference
    After
    Public exploit reference
    github.com ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2026-42697↗CISA Vulnrichment SSVC evidence↗Public exploit reference · GitHub GHSA-G4F7-W2RC-HPJ6↗Vendor advisory↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-21901 · cve.blacktree.nl