# What is CVE-2023-6764?

> CVE-2023-6764 is a high-severity flaw (CVSS 8.1) in Usg Flex 50 from Zyxel, published on 20 February 2024. 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 0.9%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.edgeprotect.io/what-is/cve-2023-6764

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **EdgeProtect risk score:** 48 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 8.1 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:** 0.9% (latest exploit-likelihood forecast)
- **Published:** 20 February 2024
- **Record last updated:** 21 January 2025
- **Main product:** Usg Flex 50 from Zyxel
- **Affected products:** 42

## What is CVE-2023-6764? 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

A format string vulnerability in a function of the IPSec VPN feature in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, and USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1 could allow an attacker to achieve unauthorized remote code execution by sending a sequence of specially crafted payloads containing an invalid pointer; however, such an attack would require detailed knowledge of an affected device’s memory layout and configuration.

### What kind of flaw is it?

- CWE-134: Use of Externally-Controlled Format String

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Hard: conditions must line up
- 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:H/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Is CVE-2023-6764 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 0.9%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 0.9%, 0.9%, 0.9%, 0.9%, 0.9%, 0.9%, 0.9%.

### Timeline

- 20 February 2024: Published
- 21 January 2025: Record last updated

### How EdgeProtect ranks it

CVE-2023-6764 scores **48 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: key context
- Real threat activity around it: key context

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-2023-6764?

The published record lists 42 products. Versions are as published: "4.32 to before 5.37" means from 4.32 up to, but not including, 5.37.

- [Usg Flex 50](https://www.edgeprotect.io/product/zyxel/usg_flex_50) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp100 Firmware](https://www.edgeprotect.io/product/zyxel/atp100_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Atp100w Firmware](https://www.edgeprotect.io/product/zyxel/atp100w_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Atp200 Firmware](https://www.edgeprotect.io/product/zyxel/atp200_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Atp500 Firmware](https://www.edgeprotect.io/product/zyxel/atp500_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Atp700 Firmware](https://www.edgeprotect.io/product/zyxel/atp700_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Atp800 Firmware](https://www.edgeprotect.io/product/zyxel/atp800_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.32 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 100 Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_100_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 100ax Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_100ax_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 100h Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_100h_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 100w Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_100w_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 200 Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_200_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 200h Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_200h_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 200hp Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_200hp_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 50 Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_50_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.16 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 500 Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_500_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 500h Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_500h_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 50w Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_50w_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.16 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 700 Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_700_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg Flex 700h Firmware](https://www.edgeprotect.io/product/zyxel/usg_flex_700h_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.50 to before 5.37, 5.37, 5.37-patch1
- [Usg20-VPN Firmware](https://www.edgeprotect.io/product/zyxel/usg20-vpn_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.16 to before 5.37, 5.37, 5.37-patch1
- [Usg20w-VPN Firmware](https://www.edgeprotect.io/product/zyxel/usg20w-vpn_firmware) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Operating system): 4.16 to before 5.37, 5.37, 5.37-patch1
- [Atp100](https://www.edgeprotect.io/product/zyxel/atp100) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp100w](https://www.edgeprotect.io/product/zyxel/atp100w) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp200](https://www.edgeprotect.io/product/zyxel/atp200) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp500](https://www.edgeprotect.io/product/zyxel/atp500) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp700](https://www.edgeprotect.io/product/zyxel/atp700) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Atp800](https://www.edgeprotect.io/product/zyxel/atp800) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 100](https://www.edgeprotect.io/product/zyxel/usg_flex_100) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 100ax](https://www.edgeprotect.io/product/zyxel/usg_flex_100ax) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 100h](https://www.edgeprotect.io/product/zyxel/usg_flex_100h) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 100w](https://www.edgeprotect.io/product/zyxel/usg_flex_100w) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 200](https://www.edgeprotect.io/product/zyxel/usg_flex_200) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 200h](https://www.edgeprotect.io/product/zyxel/usg_flex_200h) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 200hp](https://www.edgeprotect.io/product/zyxel/usg_flex_200hp) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 500](https://www.edgeprotect.io/product/zyxel/usg_flex_500) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 500h](https://www.edgeprotect.io/product/zyxel/usg_flex_500h) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 50w](https://www.edgeprotect.io/product/zyxel/usg_flex_50w) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 700](https://www.edgeprotect.io/product/zyxel/usg_flex_700) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg Flex 700h](https://www.edgeprotect.io/product/zyxel/usg_flex_700h) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg20-VPN](https://www.edgeprotect.io/product/zyxel/usg20-vpn) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified
- [Usg20w-VPN](https://www.edgeprotect.io/product/zyxel/usg20w-vpn) by [Zyxel](https://www.edgeprotect.io/vendors/zyxel) (Hardware): version not specified

## How do I fix CVE-2023-6764?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? EdgeProtect 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/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-aps-02-20-2024) (Vendor advisory)

## Questions

### What is CVE-2023-6764?

CVE-2023-6764 is a high-severity flaw in Usg Flex 50 from Zyxel, published on 20 February 2024. 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-2023-6764?

It scores 8.1 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2023-6764 is 48 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2023-6764 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 0.9%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2023-6764 affect?

For Usg Flex 50 from Zyxel: version not specified. The record lists 42 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2023-6764?

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-2023-6764 affect you?

EdgeProtect 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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