Affects widely deployed Junos SRX/MX network devices; critical infrastructure exposure; notable DoS risk.
CVE-2026-21905
DoS via infinite loop in Junos SIP ALG on SRX/MX (TCP SIP), unauthenticated.
Is CVE-2026-21905 being exploited?
Not confirmed. CVE-2026-21905 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.42% probability of exploitation in the next 30 days.
How severe is CVE-2026-21905?
CVE-2026-21905 is rated High with a CVSS score of 8.7. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-21905?
Yes. A fix has been recorded for CVE-2026-21905. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-21905 affect?
CVE-2026-21905 affects Juniper Junos OS on SRX Series, Juniper Junos OS on MX Series with MX-SPC3 or MS-MPC cards. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-21905?
Upgrade to fixed Junos OS release per Juniper advisory
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated remote DoS: TCP SIP messages crash flowd/mspmand, causing network device outage.
Immediate action required
- affected< 21.2R3-S10
- affected>= 21.4 and < 21.4R3-S12
- affected>= 22.4 and < 22.4R3-S8
- affected>= 23.2 and < 23.2R2-S5
- affected>= 23.4 and < 23.4R2-S6
- affected>= 24.2 and < 24.2R2-S3
- affected>= 24.4 and < 24.4R2-S1
- affected>= 25.2 and < 25.2R1-S1, 25.2R2
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.