CISA sunsets 10 emergency directives thanks to evolution of exploited vulnerabilities catalog

CVE-2020-0601 (known as 'Curveball') is a spoofing flaw in Crypt32.dll, the Windows CryptoAPI component that validates Elliptic Curve Cryptography (ECC) certificates, which mishandles ECC certificate parameters when checking signatures. An attacker can trigger it by signing malicious content, most notably an executable, with a spoofed, attacker-controlled ECC certificate that Windows accepts as if it were issued by a trusted certificate authority; the attack vector is network-based but requires user interaction (CVSS 3.1: 8.1, AV:N/AC:L/PR:N/UI:R). Successful exploitation makes attacker-supplied malware appear to come from a legitimate, trusted software vendor, defeating code-signing trust prompts and signature-based trust decisions, with high impact on confidentiality and integrity. Affected systems are the Microsoft Windows 10 builds 1507 through 1909 and Windows Server versions 1803, 1903, 1909, 2016 and 2019 in the CISA data, with Go also listed as an affected vendor via its ECC certificate validation, effectively covering the mainstream Windows install base at the time. The flaw was discovered by the NSA and patched in the January 2020 Patch Tuesday; it is now CISA KEV-listed (added 2021-11-03, ransomware use unknown) with very high predicted exploitation risk (EPSS 89.4%, 100th percentile), and no public PoC is tracked in this data.

Do: Apply Microsoft's January 2020 Patch Tuesday cumulative security updates for all affected Windows 10 and Windows Server builds, per CISA's required action (apply updates per vendor instructions). Prioritize user workstations and servers that validate signed binaries, Authenticode signatures, or TLS certificates, since exploitation hinges on a user or application trusting a spoofed ECC-signed artifact. If Go is deployed in your environment, update Go toolchains to a patched January 2020 or later release, as Go was also acknowledged as an affected vendor.

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.

Ivanti Pulse Connect Secure, a widely deployed SSL VPN appliance, contains a use-after-free vulnerability in its license services. A remote, unauthenticated attacker can trigger the flaw via the license services and gain arbitrary code execution on the appliance, which is a high-value target because it terminates VPN sessions for enterprise networks. Any organization running an affected Pulse Connect Secure release is potentially affected; the source data does not specify exact version ranges, so administrators should compare their release against Ivanti's advisory. Exploitation is confirmed in the wild: the flaw is on CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) with known ransomware use, and its 47.2% EPSS score (99th percentile) indicates a high likelihood of exploitation within 30 days.

Do: Apply the updates per Ivanti's instructions immediately, as CISA's required action specifies. Because exploited appliances have often retained persistent webshells/backdoors even after patching, also hunt for indicators of compromise (modified appliance files, unexpected processes or accounts) and follow Ivanti's remediation guidance rather than only installing the update. Until patched, restrict or closely monitor internet access to the appliance.

CVE-2021-26855 is a server-side request forgery flaw (CWE-918) in Microsoft Exchange Server that allows an unauthenticated remote attacker to send specially crafted HTTP requests and have the Exchange server process them as itself, disclosing sensitive session information. When chained with sibling Exchange flaws (the 'ProxyLogon' chain), it yields authentication bypass and arbitrary file write, escalating to full remote code execution with SYSTEM-level privileges on the on-premises Exchange server. Any organization running an affected on-premises Exchange server reachable over HTTP/HTTPS (typically outbound webmail) is exposed; Exchange Online was not affected. Exploitation is confirmed in the wild at large scale: the flaw was mass-exploited beginning in early 2021 (notably by the HAFNIUM group), is on the CISA KEV with documented ransomware use, and has a maximum EPSS score of 100% (100th percentile), despite no public PoC listing.

Do: Apply the vendor's March 2021 Exchange security updates (or later cumulative updates) immediately, per the CISA required action; until patched, limit Exchange (ECP/OWA) exposure to the internet via firewall/VPN rules. Hunt for compromise: review IIS logs for unrecognized authenticated activity against FrontEnd HttpProxy endpoints, and check for malicious files or webshells under inetpub\wwwroot\aspnet_client, given the known ransomware use.

CVE-2021-34527, widely known as 'PrintNightmare', is a remote code execution flaw in the Microsoft Windows Print Spooler service, which improperly performs privileged file operations such as loading printer driver DLLs. An attacker with low-level access who can reach a machine's spooler, for example a domain user able to add a printer connection via Point and Print, can induce the SYSTEM-privileged service to load an attacker-controlled DLL with no user interaction required (CVSS:3.1 vector AV:N/AC:L/PR:L/UI:N). Successful exploitation yields arbitrary code execution as SYSTEM, letting the attacker install programs, view, change or delete data, and create new accounts with full user rights, effectively achieving complete host compromise. The flaw affects all supported Windows client and server releases in the CISA data, Windows 10 from 1507 through 22H2, Windows 11, Windows RT 8.1, and Windows Server 2008, 2012 and 2016, wherever the Print Spooler service is running. Exploitation is confirmed in the wild: the bug was added to CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 with known ransomware use, the FBI and CISA have warned of Russian actors exploiting it, and EPSS places the 30-day exploitation probability at 99.8%.

Do: Install the July 2021 security updates immediately, released July 6, 2021 with additional updates on July 7 for Windows Server 2012, Windows Server 2016 and Windows 10 version 1607, and review KB5005010 for restricting installation of new printer drivers after applying the July 6 updates. Where patching is delayed, disable the Print Spooler service on hosts that do not need printing or restrict Point and Print, and verify that NoWarningNoElevationOnInstall and UpdatePromptSettings under HKLM\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint are set to 0 or not defined (these keys do not exist by default, which is the secure state; NoWarningNoElevationOnInstall = 1 makes the system vulnerable by design). Prioritize domain controllers and servers with exposed spoolers, and hunt…