# CVE-2019-1739: Cisco IOS and IOS XE Software Network-Based Application Recognition Denial of Service Vulnerabilities

> Remote attackers can cause Cisco IOS devices to reload by sending crafted DNS packets if NBAR is enabled, resulting in a denial of service.

- **Severity:** High 8.6 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Mar 2019
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-2xhp-rj78-v5hh

## What is CVE-2019-1739?

CVE-2019-1739 is a high-severity denial of service vulnerability in Cisco Ios, published on 27 Mar 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the Network-Based Application Recognition (NBAR) feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. This vulnerability is due to a parsing issue on DNS packets. An attacker could exploit this vulnerability by sending crafted DNS packets through routers that are running an affected version and have NBAR enabled. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2019-1739?

It affects 2 products.


Products: Cisco Ios, Cisco Ios Xe.

## How do I fix CVE-2019-1739?

No fix has been published for CVE-2019-1739 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-1739 being exploited?

There is no known exploitation of CVE-2019-1739 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios

- [CVE-2017-12240](https://insights.sbomify.com/CVE-2017-12240/): Cisco IOS and IOS XE Software DHCP Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2017-3881](https://insights.sbomify.com/CVE-2017-3881/): Cisco IOS and IOS XE Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2018-0167](https://insights.sbomify.com/CVE-2018-0167/): Cisco IOS, XR, and XE Software Buffer Overflow (high 8.8, exploited in the wild)
- [CVE-2017-6736](https://insights.sbomify.com/CVE-2017-6736/): Cisco IOS and IOS XE Software SNMP Remote Code Execution (high 8.8, exploited in the wild)
- [CVE-2017-6737](https://insights.sbomify.com/CVE-2017-6737/): Cisco IOS and IOS XE Software SNMP Remote Code Execution (high 8.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-1739 and fix it if it is affected.

What it is: CVE-2019-1739 is a high-severity denial of service vulnerability in Cisco Ios, published on 27 Mar 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-2019-1739 in the wild and no public exploit code.

Affected product: Cisco Ios. 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-2019-1739/ (Markdown: https://insights.sbomify.com/CVE-2019-1739/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-1739
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-1739
- OSV: https://osv.dev/vulnerability/CVE-2019-1739

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From sbomify Insights: https://insights.sbomify.com/CVE-2019-1739/
Summaries are generated and may contain mistakes; the official description above is the record.