June 5: 2 New Vulns | CVE-2023-33009, CVE-2023-33010
In this CISA KEV Breakdown, two vulnerabilities affecting the same set of Zyxel technologies as CVE-2023-28771 have been added to the KEV catalog. The two vulnerabilities can be exploited remotely and unauthenticated, so users possibly affected are encouraged to patch to the latest fixed versions as soon as possible. The patch for CVE-2023-28771 was released late April, with these two vulnerabilities having their advisory posted just last month on the 24th.
Some readers may remember our Breakdown post covering CVE-2023-28771, in which Mirai botnet scoured the internet for susceptible targets to exploit. Currently available evidence surrounding exploitation points to the likelihood that these vulnerabilities are also being used to further Mirai botnet campaign efforts. For organizations with affected devices, users are encouraged to triage potentially compromised Zyxel hardware for anomalous outbound traffic.
CVE ID | Vendor/Project | Software | Exploitation Consequence | GreyNoise Traffic | EPSS Score | EPSS Percentile | Due Date |
CVE-2023-33009 | Zyxel | Multiple Firewall products | Remote Code Execution | 0.00091 | 37.81% | 06/26/2023 | |
CVE-2023-33010 | Zyxel | Multiple Firewall products | Remote Code Execution | 0.00091 | 37.81% | 06/26/2023 |
Notable Vulnerability Additions
CVE-2023-33009 | Zyxel Firewalls Buffer Overflow
A vulnerability in the notification function of Zyxel firmware could allow an unauthenticated attacker to cause remote code execution, with failed exploitation likely leading to denial-of-service.
The following Zyxel technologies are reported as vulnerable: Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 through 4.73 Patch 1.
No public exploit code appears to exist at this time, and there is little evidence publicly available as to exploitation activity that resulted in this vulnerability’s addition to the KEV.
Security Advisory(s):
CVE-2023-33010 | Zyxel Firewalls Buffer Overflow
Much of what is described here will echo what is written above for CVE-2023-33009, as these are very similar vulnerabilities in nature, but deserving of two distinct CVE IDs due to the fact that the resulting exploitation derives from separate functionality and components.
A vulnerability found in the ID processing function in Zyxel firmware could allow an unauthenticated attacker to cause remote code execution, with failed exploitation likely leading to a denial-of-service.
The following Zyxel technologies are reported as vulnerable: Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX series firmware versions 4.50 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.25 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.25 through 5.36 Patch 1, VPN series firmware versions 4.30 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.25 through 4.73 Patch 1.
Much like CVE-2023-33009, no public exploit code appears available at time of writing, and little evidence exists as to the active exploitation observed by CISA.
GreyNoise has launched a tag to observe Zyxel RCE scanning attempts which can be found here.
Security Advisory(s):
While assumptions shouldn’t be considered a threat analyst’s best friend, existing evidence surrounding the exploitation of these vulnerabilities indicates a similar goal to the exploitation of CVE-2023-28771. Zyxel has released a more recent advisory on June 2nd, lumping together CVE-2023-28771 with the two vulnerabilities described in this breakdown, which can be viewed here. Hackers and defenders alike appreciate many different things, but one thing can surely be found in both parties: Taking the path of least resistance to drive results and action.
← June 2, 2023 CISA Kev Breakdown
Click here to expand our CISA KEV Breakdown Frequently Asked Questions
- What makes for a notable addition?
- A notable addition can arise from many different characteristics. If a particular vulnerability is notable to the security community or a subset of the security community or if the EPSS score reveals notable information about the vulnerability, this can constitute further analysis. It may also be the case that a particular vulnerability shines a light on everyday users and we will highlight important information and key takeaways to ensure users and readers have easy access to actionable information.
- When is the Breakdown released?
- We aim to have our analysis of each KEV update posted within 24 hours of the time in which the Catalog is updated. See CISA’s full catalog here
- I am not bound by BOD 22-01 or federal regulations, why should the KEV concern me?
- CISA encourages all organizations to utilize the Catalog as an attribute in your vulnerability prioritization framework. Organizations looking to lessen the scope on known dangerous vulnerabilities and make a goal to remediate them can understand where they currently stand against what CISA has confirmed as exploited vulnerabilities in the wild. See CISA’s section on “How should organizations use the KEV catalog?” here.
- What is EPSS?
- EPSS is the Exploit Prediction Scoring System. It is an open, data-driven effort for estimating the likelihood (probability) that a software vulnerability will be exploited in the wild. See the EPSS home page on FIRST for more information here.
- What is the difference between EPSS probability and EPSS percent?
- EPSS probability is the risk calculated by the model when determining the perceived threat of the vulnerability itself. Percentage is a relative comparison of the rest of the CVEs within the given sample. While the probability only changes upon refreshing the results from the model, the percentage can change purely based on the CVE sample given. In the case of the Breakdown, we use the percentage given by the pool of all CVEs with given EPSS data. Scores may vary post-release of the post given new information about the vulnerabilities and their perceived threat. For more information on applying and understanding EPSS data, see this article on the FIRST website, as well as their FAQ page.
- What is GreyNoise?
- GreyNoise is a platform that collects, analyzes, and labels data on IPs that scan the internet and saturate security tools with noise. Through their sensor network, GreyNoise observes vulnerability exploitation attempts for vulnerabilities that are exploited in the wild over the Internet. These are arguably vulnerabilities that should be at the very top of your priority list to remediate.
- Why are GreyNoise exploitation attempts only observed on ~20% of KEV vulnerabilities?
- Exploitation of many vulnerabilities in the CISA KEV will not be observed for many reasons that GreyNoise does a good job of explaining in this post. For example:
- The vulnerability may not be remotely exploitable
- Vulnerability exploitation may require authentication (and result in privilege escalation)
- The impacted software may not be exposed to the internet
- Mass scanning/exploitation is not occurring yet
- Exploitation of many vulnerabilities in the CISA KEV will not be observed for many reasons that GreyNoise does a good job of explaining in this post. For example: