# 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.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/AU:Y/R:A/RE:M`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jul 2026
- **Updated:** 10 Jul 2026
- **Also known as:** GHSA-8p3c-wvj4-2gqc

## 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 (Improper Validation of Specified Quantity in Input)

## Which versions are affected by CVE-2026-57023?

It affects 1 product.


Products: 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.

## 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](https://insights.sbomify.com/CVE-2023-36845/): Juniper Junos OS EX Series and SRX Series PHP External Variable Modification (critical 9.8, exploited in the wild)
- [CVE-2020-1631](https://insights.sbomify.com/CVE-2020-1631/): Juniper Junos OS Path Traversal (high 8.8, exploited in the wild)
- [CVE-2025-21590](https://insights.sbomify.com/CVE-2025-21590/): Juniper Junos OS Improper Isolation or Compartmentalization (medium 6.7, exploited in the wild)
- [CVE-2023-36851](https://insights.sbomify.com/CVE-2023-36851/): Juniper Junos OS SRX Series Missing Authentication for Critical Function (medium 5.3, exploited in the wild)
- [CVE-2023-36844](https://insights.sbomify.com/CVE-2023-36844/): Juniper Junos OS EX Series PHP External Variable Modification (medium 5.3, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-57023 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-57023 in the wild and no public exploit code.

Affected product: Juniper Junos. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-57023/ (Markdown: https://insights.sbomify.com/CVE-2026-57023/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-57023
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-57023
- OSV: https://osv.dev/vulnerability/CVE-2026-57023

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-57023/
Summaries are generated and may contain mistakes; the official description above is the record.