Unauthenticated DoS on core routing/firewall devices could disrupt networks; Junos SRX/MX widely deployed.
CVE-2026-21918
Unauthenticated DoS via double-free in Junos flowd on SRX/MX.
Is CVE-2026-21918 being exploited?
Not confirmed. CVE-2026-21918 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 0.41% probability of exploitation in the next 30 days.
How severe is CVE-2026-21918?
CVE-2026-21918 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-2026-21918?
Yes. A fix has been recorded for CVE-2026-21918. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-21918 affect?
CVE-2026-21918 affects Juniper SRX Series, Juniper MX Series, Junos OS flowd. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-21918?
Patch to fixed Junos OS release per vendor advisories.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated network DoS: flowd double-free during TCP session setup crashes flowd and restarts FPC, causing downtime.
Immediate action required
- affected< 22.4R3-S7
- affected>= 23.2 and < 23.2R2-S3
- affected>= 23.4 and < 23.4R2-S4
- affected>= 24.2 and < 24.2R2
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.