# What is CVE-2019-15800?

> CVE-2019-15800 is a critical-severity flaw (CVSS 9.8) in Gs1900-8 Firmware from Zyxel, published on 14 November 2019. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 3.9%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2019-15800

## At a glance

- **Verdict:** Fix this soon. Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month.
- **Precursor Intelligence risk score:** 61 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** Critical (CVSS 9.8 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 3.9% (latest exploit-likelihood forecast)
- **Published:** 14 November 2019
- **Record last updated:** 24 August 2020
- **Main product:** Gs1900-8 Firmware from Zyxel
- **Affected products:** 18

## What is CVE-2019-15800? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### The official description

An issue was discovered on Zyxel GS1900 devices with firmware before 2.50(AAHH.0)C0. Due to lack of input validation in the cmd_sys_traceroute_exec(), cmd_sys_arp_clear(), and cmd_sys_ping_exec() functions in the libclicmd.so library contained in the firmware, an attacker could leverage these functions to call system() and execute arbitrary commands on the switches. (Note that these functions are currently not called in this version of the firmware, however an attacker could use other vulnerabilities to finally use these vulnerabilities to gain code execution.)

### What kind of flaw is it?

- CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can read data, change data and take it offline

Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Is CVE-2019-15800 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 3.9%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 3.9%, 3.9%, 3.9%, 3.9%, 3.9%, 3.9%, 3.9%.

### Timeline

- 14 November 2019: Published
- 24 August 2020: Record last updated

### How Precursor Intelligence ranks it

CVE-2019-15800 scores **61 out of 100 (Medium)**, with the action "Plan remediation".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2019-15800?

The published record lists 18 products. Versions are as published: "before 2.50(aahh.0)c0" means every version up to, but not including, 2.50(aahh.0)c0.

- [Gs1900-8 Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-8_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahh.0)c0
- [Gs1900-10hp](https://www.precursorintelligence.com/product/zyxel/gs1900-10hp) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-10hp Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-10hp_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aazi.0)c0
- [Gs1900-16](https://www.precursorintelligence.com/product/zyxel/gs1900-16) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-16 Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-16_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahj.0)c0
- [Gs1900-24](https://www.precursorintelligence.com/product/zyxel/gs1900-24) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-24 Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-24_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahl.0)c0
- [Gs1900-24e](https://www.precursorintelligence.com/product/zyxel/gs1900-24e) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-24e Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-24e_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahk.0)c0
- [Gs1900-24hp](https://www.precursorintelligence.com/product/zyxel/gs1900-24hp) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-24hp Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-24hp_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahm.0)c0
- [Gs1900-48](https://www.precursorintelligence.com/product/zyxel/gs1900-48) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-48 Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-48_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahn.0)c0
- [Gs1900-48hp](https://www.precursorintelligence.com/product/zyxel/gs1900-48hp) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-48hp Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-48hp_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aaho.0)c0
- [Gs1900-8](https://www.precursorintelligence.com/product/zyxel/gs1900-8) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-8hp](https://www.precursorintelligence.com/product/zyxel/gs1900-8hp) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Hardware): version not specified
- [Gs1900-8hp Firmware](https://www.precursorintelligence.com/product/zyxel/gs1900-8hp_firmware) by [Zyxel](https://www.precursorintelligence.com/vendors/zyxel) (Operating system): before 2.50(aahi.0)c0

## How do I fix CVE-2019-15800?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [zyxel.com](https://www.zyxel.com/support/gs1900-switch-vulnerabilities.shtml) (Vendor advisory)
- [jasper.la](https://jasper.la/exploring-zyxel-gs1900-firmware-with-ghidra.html) (Exploit, Third-party advisory)

## Questions

### What is CVE-2019-15800?

CVE-2019-15800 is a critical-severity flaw in Gs1900-8 Firmware from Zyxel, published on 14 November 2019. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.

### How serious is CVE-2019-15800?

It scores 9.8 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2019-15800 is 61 out of 100, which is Medium. Its action is "Plan remediation". Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month.

### Is CVE-2019-15800 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 3.9%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2019-15800 affect?

For Gs1900-8 Firmware from Zyxel: before 2.50(aahh.0)c0. The record lists 18 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2019-15800?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2019-15800 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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