CVE-2026-21901

Description

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.

PUBLISHED Reserved 2026-01-05 | Published 2026-07-09 | Updated 2026-07-10 | Assigner juniper

Problem types

CWE-476 NULL Pointer Dereference

Product status

Credits

Juniper SIRT would like to acknowledge and thank Orange CERT-CC from the Orange group for responsibly reporting this vulnerability. finder

References

github.com/...search/security/advisories/GHSA-g4f7-w2rc-hpj6 exploit

github.com/...search/security/advisories/GHSA-g4f7-w2rc-hpj6 third-party-advisory

supportportal.juniper.net/JSA110072 vendor-advisory

cve.org (CVE-2026-21901)

nvd.nist.gov (CVE-2026-21901)

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