Zyxel firewalls under attack by Mirai-like botnet
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2023-28771 | Unauthenticated OS Command Injection in Zyxel ATP, USG FLEX, VPN, and ZyWALL Firewalls CVE-2023-28771 is an unauthenticated OS command injection flaw (CWE-78) in Zyxel firewall firmware, caused by improper error message handling in the IKE packet decoder. A remote attacker triggers it by sending crafted packets to an affected device, with no credentials or user interaction required (CVSS 3.1: 9.8, network vector, low complexity). Successful exploitation lets the attacker execute operating-system commands on the firewall, which typically means full device compromise of these perimeter/VPN gateway appliances. Organizations running Zyxel ZyWALL/USG, VPN, USG FLEX, or ATP series firewalls on the affected firmware ranges are exposed, especially where IKE/VPN traffic is reachable from the internet. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV on 2023-05-31, carries a 99.3% EPSS score (100th percentile), is reportedly used by DDoS botnets, and was reportedly exploited in the May 2023 coordinated attacks against nearly two dozen Danish energy companies. Do: Apply Zyxel's patched firmware to all affected devices per the vendor advisory - releases newer than 4.73 for ZyWALL/USG and newer than 5.35 for ATP, USG FLEX, and VPN series - prioritizing internet-facing and VPN gateway appliances, as this is a KEV required-action vulnerability. Where immediate patching is not possible, restrict IKE traffic (UDP 500/4500) to trusted peers or disable unneeded IPsec VPN termination. After patching, review device logs and configurations for signs of command execution or unexpected changes, given confirmed botnet and targeted-attack use. | 9.8 | 99% | KEV PoC |
| largetens of thousands of internet-exposed Zyxel firewall/VPN gateways (order of 10,000-100,000 devices/sites); estimate | |
| CVE-2023-33010 +1 in the same advisory: …33009 | Buffer Overflow in Zyxel ATP, USG FLEX, VPN and ZyWALL/USG Firewalls Enables RCE CVE-2023-33010 is a buffer overflow (CWE-120) in the ID processing function of Zyxel's firewall firmware that is triggered when an affected device processes crafted input sent by an unauthenticated attacker. Successful exploitation can cause denial-of-service conditions and, more seriously, allow remote code execution on the firewall itself, giving an attacker a foothold at the network perimeter. The flaw affects multiple Zyxel firewall lines widely used by small and mid-sized organizations, including ATP, USG FLEX, USG FLEX 50(W), USG20(W)-VPN, VPN, and legacy ZyWALL/USG models. The vulnerability has been added to CISA's Known Exploited Vulnerabilities catalog (added 2023-06-05), indicating it is being exploited in the wild, though no public proof-of-concept is known and ransomware association is unconfirmed. EPSS puts the 30-day exploitation probability at 28.8% (98th percentile), and no CVSS score has been published yet. Do: Apply the updated firmware for your specific model per Zyxel's security advisory, since the CISA required action is to patch per vendor instructions. Until patched, restrict or disable WAN-side access to the firewall's management/ID processing interfaces and monitor devices for signs of compromise such as unexpected reboots or crashes. Inventory all ATP, USG FLEX (including 50(W)), USG20(W)-VPN, VPN, and ZyWALL/USG units to confirm none remain unpatched. | 9.8 | 29% | KEV |
| large≈tens of thousands of internet-exposed devices from a combined installed base likely well over 100,000 across these firewall lines |
Full article403 words · extracted from helpnetsecurity.com · click to collapse
CVE-2023-28771, the critical command injection vulnerability affecting many Zyxel firewalls, is being actively exploited by a Mirai-like botnet, and has been added to CISA’s Known Exploited Vulnerabilities (KEV) catalog.
About CVE-2023-28771
CVE-2023-28771 is a vulnerability that allows unauthenticated attackers to execute OS commands remotely by sending crafted IKE (Internet Key Exchange) packets to an affected device.
Fixed by Zyxel in April 2023, it was expected to be quickly exploited by attackers once technical write-ups and PoCs are made public – and so it happened.
“While Internet Key Exchange (IKE) is the protocol used to initiate this exploit, it’s not a vulnerability in IKE itself, but it seems to be a result of this rogue debugging function that shouldn’t have made it into a production build of the firmware. But since IKE is the only known protocol where the path to this vulnerability can be triggered, it’s much more likely that only the Zyxel devices that are running IKE are actually vulnerable to this attack,” Censys researchers explained.
“This vulnerability stems from a problematic logging function. Instead of employing a secure file handling mechanism by opening up a file handle and writing data to that handle, Zyxel chose a different approach: They constructed an “echo” command by incorporating user-controlled input data. This echo command is subsequently executed through a system() call, writing the output to a file in /tmp. This implementation introduces an OS command injection vector, as the command construction process can be influenced by user-controllable input, and there is no data sanitization.”
CVE-2023-28771 exploited
Exploitation attempts started around May 25 and are being tracked by various cybersecurity companies and organizations.
Censys pinpointed 21,210 potentially vulnerable devices around the world, but predominantly in Europe (i.e., Italy, France, and Switzerland).
“These devices are deployed in all sorts of residential and business networks, both large and small. So the majority of networks these devices can be found in will be telecoms and other types of service providers,” they noted.
Vulnerable devices that haven’t been patched by now should be considered compromised and are already being leveraged in attacks (e.g., DDoS attacks).
Users who don’t know how to remediate the compromise should ask for help from their service provider. Those who have implemented the necessary update in time are advised to update again: Zyxel has relased new patches to fix two buffer overflow flaws (CVE-2023-33009, CVE-2023-33010) in those same firewalls on May 24.
Text extracted automatically; images, tables and formatting may be missing. Original: https://www.helpnetsecurity.com/2023/06/01/cve-2023-28771-exploited/