# CVE-2019-1686: Cisco ASR 9000 Series Aggregation Services Routers ACL Bypass Vulnerability

> Remote attackers can bypass ACL protections on Cisco ASR 9000 routers when specific load balancing settings are enabled.

- **Severity:** Medium 5.8 (`CVSS:3.0/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:** 17 Apr 2019
- **Updated:** 19 Nov 2024
- **Also known as:** GHSA-9wr9-3p7g-gc32

## What is CVE-2019-1686?

CVE-2019-1686 is a medium-severity vulnerability in Cisco Ios Xr, published on 17 Apr 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the TCP flags inspection feature for access control lists (ACLs) on Cisco ASR 9000 Series Aggregation Services Routers could allow an unauthenticated, remote attacker to bypass protection offered by a configured ACL on an affected device. The vulnerability is due to incorrect processing of the ACL applied to an interface of an affected device when Cisco Express Forwarding load balancing using the 3-tuple hash algorithm is enabled. An attacker could exploit this vulnerability by sending traffic through an affected device that should otherwise be denied by the configured ACL. An exploit could allow the attacker to bypass protection offered by a configured ACL on the affected device. There are workarounds that address this vulnerability. Affected Cisco IOS XR versions are: Cisco IOS XR Software Release 5.1.1 and later till first fixed. First Fixed Releases: 6.5.2 and later, 6.6.1 and later.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2019-1686?

It affects 1 product.


Products: Cisco Ios Xr.

## How do I fix CVE-2019-1686?

No fix has been published for CVE-2019-1686 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-1686 being exploited?

There is no known exploitation of CVE-2019-1686 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios Xr

- [CVE-2020-3118](https://insights.sbomify.com/CVE-2020-3118/): Cisco IOS XR Software Discovery Protocol Format String (high 8.8, exploited in the wild)
- [CVE-2020-3569](https://insights.sbomify.com/CVE-2020-3569/): Cisco IOS XR Software DVMRP Memory Exhaustion (high 8.6, exploited in the wild)
- [CVE-2020-3566](https://insights.sbomify.com/CVE-2020-3566/): Cisco IOS XR Software DVMRP Memory Exhaustion (high 8.6, exploited in the wild)
- [CVE-2010-3035](https://insights.sbomify.com/CVE-2010-3035/): Cisco IOS XR Border Gateway Protocol (BGP) Denial-of-Service (high 7.5, exploited in the wild)
- [CVE-2022-20821](https://insights.sbomify.com/CVE-2022-20821/): Cisco IOS XR Open Port (medium 6.5, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-1686 and fix it if it is affected.

What it is: CVE-2019-1686 is a medium-severity vulnerability in Cisco Ios Xr, published on 17 Apr 2019. 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-2019-1686 in the wild and no public exploit code.

Affected product: Cisco Ios Xr. 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-2019-1686/ (Markdown: https://insights.sbomify.com/CVE-2019-1686/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-1686
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-1686
- OSV: https://osv.dev/vulnerability/CVE-2019-1686

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-1686/
Summaries are generated and may contain mistakes; the official description above is the record.