CVE-2026-57023 Junos OS: MX with SPC3, SRX Series: A specifically malformed TCP packet causes a flowd crash
An unauthenticated attacker can cause a complete service outage on Juniper MX and SRX devices by sending a malformed TCP packet when TCP proxy features are active.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-57023?
CVE-2026-57023 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-1284
Which versions are affected by CVE-2026-57023?
It affects 1 product.
Products include Juniper Junos.
How do I fix CVE-2026-57023?
No fix has been published for CVE-2026-57023 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-57023 being exploited?
There is no known exploitation of CVE-2026-57023 in the wild and no public exploit code.
Other vulnerabilities in Juniper Junos
- CVE-2023-36845 Juniper Junos OS EX Series and SRX Series PHP External Variable Modification
- CVE-2020-1631 Juniper Junos OS Path Traversal
- CVE-2025-21590 Juniper Junos OS Improper Isolation or Compartmentalization
- CVE-2023-36851 Juniper Junos OS SRX Series Missing Authentication for Critical Function
- CVE-2023-36844 Juniper Junos OS EX Series PHP External Variable Modification
Sources
Also known as GHSA-8p3c-wvj4-2gqc.