# CVE-2021-28511: Security feature bypass in EOS

> Attackers can bypass security ACL drop rules if a NAT ACL permit rule matches, allowing unauthorized traffic forwarding on Arista EOS devices.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Aug 2022
- **Updated:** 2 Jun 2026
- **Also known as:** GHSA-7rjh-m68p-34pq

## What is CVE-2021-28511?

CVE-2021-28511 is a medium-severity vulnerability in Arista Networks EOS, published on 5 Aug 2022. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

This advisory documents the impact of an internally found vulnerability in Arista EOS for security ACL bypass. The impact of this vulnerability is that the security ACL drop rule might be bypassed if a NAT ACL rule filter with permit action matches the packet flow. This could allow a host with an IP address in a range that matches the range allowed by a NAT ACL and a range denied by a Security ACL to be forwarded incorrectly as it should have been denied by the Security ACL. This can enable an ACL bypass.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-28511?

It affects 1 product.


Products: Arista Eos.

## How do I fix CVE-2021-28511?

No fix has been published for CVE-2021-28511 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-28511 being exploited?

There is no known exploitation of CVE-2021-28511 in the wild and no public exploit code.

## Other vulnerabilities in Arista Networks EOS

- [CVE-2026-7473](https://insights.sbomify.com/CVE-2026-7473/): Arista Extensible Operating System Incomplete Comparison with Missing Factors (medium 6.9, exploited in the wild)
- [CVE-2015-8236](https://insights.sbomify.com/CVE-2015-8236/): Privilege escalation in n/a (critical 10.0)
- [CVE-2020-10188](https://insights.sbomify.com/CVE-2020-10188/): Memory corruption in n/a (critical 9.8)
- [CVE-2017-18017](https://insights.sbomify.com/CVE-2017-18017/): Use after free in n/a (critical 9.8)
- [CVE-2017-14491](https://insights.sbomify.com/CVE-2017-14491/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-28511 and fix it if it is affected.

What it is: CVE-2021-28511 is a medium-severity vulnerability in Arista Networks EOS, published on 5 Aug 2022. 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-2021-28511 in the wild and no public exploit code.

Affected product: Arista Networks EOS. 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-2021-28511/ (Markdown: https://insights.sbomify.com/CVE-2021-28511/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-28511
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-28511
- OSV: https://osv.dev/vulnerability/CVE-2021-28511

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-28511/
Summaries are generated and may contain mistakes; the official description above is the record.