NSA: Patch These 25 CVEs Exploited by Chinese Attackers

CVE-2019-0708 is a use-after-free (CWE-416) vulnerability in Microsoft Remote Desktop Services, formerly Terminal Services, in which an unauthenticated attacker can connect to a target system over RDP and send specially crafted requests to trigger the flaw. Because the trigger requires no authentication, the flaw is wormable: a successful exploit grants remote code execution on the target host, potentially with elevated privileges, and could allow self-propagating attacks similar to WannaCry. Organizations running the affected Microsoft Remote Desktop Services, particularly legacy Windows releases still accepting inbound RDP connections, are in scope. Exploitation is confirmed in the wild: the flaw (nicknamed BlueKeep) is listed in CISA's KEV catalog (added 2021-11-03), CISA notes known ransomware use, and EPSS assigns it a 100% probability of exploitation within 30 days.

Do: Apply Microsoft's security updates for CVE-2019-0708 per vendor instructions, prioritizing legacy or end-of-support Windows systems exposed to inbound RDP. As mitigation, restrict RDP (TCP 3389) to trusted networks or VPN access, require Network Level Authentication (NLA), and audit perimeter firewalls and public scans for open RDP listeners. The vulnerability is in the CISA KEV catalog, so patching is treated as a required action for federal and high-risk environments.

Ivanti Pulse Connect Secure, an enterprise SSL VPN appliance, contains an arbitrary file read vulnerability (CWE-22, path traversal) that requires no authentication. An unauthenticated remote attacker with network access to the appliance over HTTPS can send a specially crafted URI containing traversal sequences to read arbitrary files from the device. The attacker gains access to sensitive appliance files, potentially including configuration or credential material useful for further compromise, and CISA records known ransomware use of this flaw. Any organization running Pulse Connect Secure, especially gateways exposed to the internet for remote access, is affected. Exploitation is established: CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2021-11-03 with known ransomware use, EPSS assigns a 100% probability of exploitation in the next 30 days, and no public PoC is known.

Do: Apply updates per Ivanti's instructions, the required action in the CISA KEV entry, prioritizing internet-facing Pulse Connect Secure gateways, and consult the vendor advisory for the applicable fixed release since no version range is provided here. Where patching is not immediate, restrict HTTPS access to the appliance and hunt for signs of exploitation (unexpected file reads, anomalous VPN logins or sessions, and follow-on ransomware activity), as CISA reports known ransomware use.

CVE-2019-19781 is a path-traversal flaw (classified CWE-22, though CISA's description calls it unspecified) in Citrix ADC (formerly NetScaler ADC), Citrix Gateway, and Citrix SD-WAN WANOP appliances that lets an unauthenticated remote attacker traverse directories via crafted requests and execute arbitrary commands on the appliance, typically with root privileges. It is triggered by sending specially crafted directory-traversal requests (crafted URLs/requests to the appliance's management or VPN endpoints), which lets the attacker write files and run commands with no credentials. Successful exploitation yields arbitrary code execution on the appliance, enabling theft of VPN/ADC credentials, lateral movement into the corporate network, and installation of persistent backdoors. Any organization running affected ADC, Gateway, or SD-WAN WANOP firmware is affected, with internet-facing gateways used for remote access at the highest risk. Exploitation is confirmed in the wild: the vulnerability is on CISA's KEV (added 2021-11-03) with known ransomware use, EPSS assigns near-certain (100.0%) probability of exploitation within 30 days, and no public PoC is listed despite confirmed abuse.

Do: Upgrade Citrix ADC, Gateway, and SD-WAN WANOP appliances to the fixed firmware builds listed in Citrix advisory CTX267020; if patching cannot be done immediately, apply Citrix's published interim mitigation and restrict internet exposure to the appliance. Because exploitation grants root code execution and persistence, after patching hunt for indicators of compromise (unexpected nsroot account, modified system files, crontab/scheduled entries), kill all active and inactive sessions, and rotate appliance and VPN credentials. Prioritize internet-facing gateways and comply with CISA's required action to apply vendor updates.

CVE-2020-1350 is a critical (CVSS 10.0) remote code execution vulnerability in the DNS Server role of Microsoft Windows Server, caused by improper input handling (CWE-20) when the server fails to properly process crafted DNS requests, notably malicious DNS signature (SIG) records delivered over TCP. An unauthenticated attacker can trigger it by sending a crafted DNS query that forces the vulnerable DNS server to perform an upstream lookup and receive a malicious response, overflowing a heap buffer. Successful exploitation yields code execution with SYSTEM privileges on the DNS server, which is very often an Active Directory domain controller, giving the attacker control of the host and typically the entire domain; the flaw is considered wormable because compromised DNS servers can propagate attacks to other servers they query. Any Windows Server 2008, 2012, 2016, or 2019 host running the DNS Server role is affected — internet-facing DNS servers are directly explovable, while internal DNS servers can be reached via malicious DNS responses passed through firewalls. The flaw was fixed in Microsoft's July 2020 updates, is listed in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03, required action: apply vendor updates), carries EPSS of 91.4% (100th percentile), and appears in the NSA's top-25 list of flaws exploited by Chinese state-sponsored hackers; no public PoC is cataloged in this dataset and ransomware use is listed as unknown.

Do: Apply the July 2020 (or later) Microsoft security updates for each affected Windows Server release, prioritizing internet-facing DNS servers and domain controllers; if patching must be delayed, apply Microsoft's registry-based workaround limiting TCP DNS packet size (TcpReceivePacketSize = 0xFF00) and restart the DNS Server service. Inventory hosts with the DNS Server role installed and review their TCP/53 exposure, especially any resolvers reachable from the internet, and confirm remediation per CISA's required action.

CVE-2020-1472, widely known as "Zerologon," is an elevation-of-privilege flaw in how the Netlogon secure channel is established over the Netlogon Remote Protocol (MS-NRPC) on Microsoft domain controllers. An unauthenticated attacker with network reachability to a domain controller sends specially crafted Netlogon messages to establish a vulnerable secure channel and then runs a specially crafted application on the network to obtain domain administrator access. Successful exploitation yields domain administrator privileges, effectively full compromise of the Active Directory environment, and the flaw is known to be used in ransomware operations. Any organization running affected Windows Server versions (2008 through 20H2) as domain controllers is exposed, along with environments using Netlogon implementations from Samba and distributions or products from Fedora, openSUSE, Canonical (Ubuntu), Debian, Synology, and Oracle. Exploitation is highly active: a public Zerologon PoC/exploit is available, the flaw is on CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03, with known ransomware use), and EPSS estimates a 99.4% probability of exploitation within 30 days.

Do: Apply the vendor updates on all domain controllers and other affected systems immediately, following Microsoft's two-phase Netlogon secure channel guidance (the enforcement phase of the phased rollout began in Q1 2021). Audit Netlogon secure-channel connections and event logs for clients still using vulnerable connections before enabling full enforcement, and install updated packages for Samba and other Netlogon implementations from Fedora, openSUSE, Ubuntu, Debian, Synology, and Oracle. Given known ransomware use, prioritize patching any domain controller reachable from user networks, VPNs, or the internet.

CVE-2020-8193 is an improper access control flaw (CWE-284/CWE-287) in Citrix ADC, Citrix Gateway, and Citrix SD-WAN WAN-OP appliances that lets an unauthenticated remote attacker reach certain URL endpoints that should require authentication. An attacker triggers it simply by sending crafted HTTP requests over the network, with no credentials or user interaction required. The direct impact is limited (CVSS 3.1 rates it 6.5 with low confidentiality and integrity impact), but access to protected endpoints can expose sensitive information and is commonly chained with other Citrix flaws; a public proof of concept for local file inclusion against Citrix ADC/NetScaler exists. Anyone running Citrix ADC or Gateway builds before 13.0-58.30, 12.1-57.18, 12.0-63.21, 11.1-64.14, or 10.5-70.18, or SD-WAN WAN-OP builds before 11.1.1a, 11.0.3d, or 10.2.7 is affected. Exploitation is confirmed in the wild: the flaw was added to CISA's Known Exploited Vulnerabilities catalog in November 2021 and was named in the NSA's list of the top 25 flaws actively exploited by Chinese state-sponsored hackers, with an EPSS probability of exploitation of 88.4%.

Do: Upgrade Citrix ADC and Citrix Gateway to at least 13.0-58.30, 12.1-57.18, 12.0-63.21, 11.1-64.14, or 10.5-70.18, and SD-WAN WAN-OP to at least 11.1.1a, 11.0.3d, or 10.2.7, per Citrix's instructions. Prioritize internet-facing ADC/Gateway appliances (VPN gateways and load balancers), since the flaw is reachable without credentials, and review appliance logs for unauthenticated access to protected endpoints. This CVE is on the CISA KEV list, so federal and KEV-committed defenders are required to apply the vendor updates.