Vulnerability in Juniper Networks Junos OS (CVE-2026-21901)
Summary
Vulnerability in Juniper Networks Junos OS (CVE-2026-21901). Risk of unauthorized operations or information disclosure.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-21901 has been found in Juniper Networks Junos OS.
Risk of unauthorized operations or information disclosure. CVSS score: 4.4/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Juniper Networks Junos OS CVE-2026-21901" on the vendor's site.
CVE-2026-21901 (Juniper Networks Junos OS) — CWE-476 / CVSS v3 4.4
Attack vector: local / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-476) exists in Juniper Networks Junos OS.
Check the vendor advisory for the affected versions of Juniper Networks Junos OS.
Severity: Medium (CVSS 4.4/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Juniper Networks Junos OS を使っているサービスとバージョンを洗い出す。
-
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
References
- exploit github.com
- patch sirt@juniper.net