# CVE-2026-57027: Junos OS: EX4100 Series, EX4400: With sFlow configured in a VC scenario multicast traffic leads to an FPC crash

> An unauthenticated adjacent attacker can cause a denial of service by triggering a memory leak in sFlow-enabled Virtual Chassis multicast traffic.

- **Severity:** High 7.1 (`CVSS:4.0/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jul 2026
- **Updated:** 10 Jul 2026
- **Also known as:** GHSA-2xj6-hwhm-5m6g

## What is CVE-2026-57027?

CVE-2026-57027 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A Missing Release of Memory after Effective Lifetime vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on specific EX Series devices allows an unauthenticated adjacent attacker to cause a Denial-of-Service (DoS).When sFlow is configured in a Virtual Chassis (VC) scenario with EX4100 Series or EX4400 Series devices, multicast traffic which is received on one VC member and sent out on another member leads to a memory leak and ultimately an FPC crash and restart.

The leak can be monitored by watching the continuous increase of the buffer values in the output of:

user@host> show chassis fpc 
This issue affects Junos OS on EX4100 Series and EX4400:

  *  all versions before 23.2R2-S7,
  *  23.4 versions before 23.4R2-S7,
  *  24.2 versions before 24.2R2-S4,
  *  24.4 versions before 24.4R2.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2026-57027?

It affects 1 product.


Products: Juniper Junos.

## How do I fix CVE-2026-57027?

No fix has been published for CVE-2026-57027 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-57027 being exploited?

There is no known exploitation of CVE-2026-57027 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-2026-57027 and fix it if it is affected.

What it is: CVE-2026-57027 is a high-severity denial of service vulnerability in Juniper Junos, published on 9 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-57027 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-2026-57027/ (Markdown: https://insights.sbomify.com/CVE-2026-57027/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-57027
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-57027
- OSV: https://osv.dev/vulnerability/CVE-2026-57027

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-57027/
Summaries are generated and may contain mistakes; the official description above is the record.