Junos OS (SRX firewalls)
CVE-2026-57023: MX with SPC3, SRX Series: A specifically malformed TCP packet causes a flowd crash
An Improper Validation of Specified Quantity in Input vulnerability in the TCP proxy plugin of Juniper Networks Junos OS on MX Series with SPC3, and SRX Series allows an unauthenticated, network-based attacker to cause a complete Denial of Service (DoS).
Published
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Junos OS (SRX Series, MX Series with SPC3) 23.4 | 23.4R2-S7 or later |
| Junos OS (SRX Series, MX Series with SPC3) 24.2 | 24.2R2-S4 or later |
| Junos OS (SRX Series, MX Series with SPC3) 24.4 | 24.4R2-S3 or later |
| Junos OS (SRX Series, MX Series with SPC3) 25.2 | 25.2R2 or later |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
An Improper Validation of Specified Quantity in Input vulnerability in the TCP proxy plugin of Juniper Networks Junos OS on MX Series with SPC3, and SRX Series allows an unauthenticated, network-based attacker to cause a complete Denial of Service (DoS).
When TCP proxy is engaged in a flow session, to support ALGs, Advanced Anti-Malware, ICAP or UTM, a TCP packet with specifically malformed TCP header will cause flow processing daemon (flowd) to crash and restart. This causes a complete service outage until the system has automatically recovered.
This issue affects Junos OS on MX with SPC3, and SRX Series:
- 23.4 versions before 23.4R2-S7,
- 24.2 versions before 24.2R2-S4,
- 24.4 versions before 24.4R2-S3,
- 25.2 versions before 25.2R2.
This issue does not affect releases before 23.4R1.
Workarounds
There are no known workarounds for this issue.
Exploitation
Juniper SIRT is not aware of any malicious exploitation of this vulnerability.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 13 Oct 2026.