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Today, CISA, the Federal Bureau of Investigation, the National Security Agency, and the U.S. Department of the Treasury released guidance on improving the security of open source software (OSS) in operational technology (OT) and industrial control systems (ICS). In alignment with CISA’s recently released Open Source Security Roadmap, the guidance provides recommendations to OT/ICS organizations on: Supporting OSS development and maintenance, Managing and patching vulnerabilities in OT/ICS environments, and Using the Cross-Sector Cybersecurity Performance Goals (CPGs) as a common framework for adopting key cybersecurity best practices in relation to OSS. Alongside the guidance, CISA published the Securing OSS in OT web page, which details the Joint Cyber Defense Collaborative (JCDC) OSS planning initiative, a priority within the JCDC 2023 Planning Agenda. The initiative will support collaboration between the public and private sectors—including the OSS community—to better understand and secure OSS use in OT/ICS, which will strengthen defense against OT/ICS cyber threats. CISA encourages OT/ICS organizations to review this guidance and implement its recommendations.

CISA has added five new vulnerabilities to its Known Exploited Vulnerabilities Catalog, based on evidence of active exploitation: CVE-2023-21608 Adobe Acrobat and Reader Use-After-Free Vulnerability CVE-2023-20109 Cisco IOS and IOS XE Group Encrypted Transport VPN Out-of-Bounds Write Vulnerability CVE-2023-41763 Microsoft Skype for Business Privilege Escalation Vulnerability CVE-2023-36563 Microsoft WordPad Information Disclosure Vulnerability CVE-2023-44487 HTTP/2 Rapid Reset Attack Vulnerability These types of vulnerabilities are frequent attack vectors for malicious cyber actors and pose significant risks to the federal enterprise. Note: To view other newly added vulnerabilities in the catalog, click on the arrow in the "Date Added to Catalog" column—which will sort by descending dates. Binding Operational Directive (BOD) 22-01: Reducing the Significant Risk of Known Exploited Vulnerabilities established the Known Exploited Vulnerabilities Catalog as a living list of known Common Vulnerabilities and Exposures (CVEs) that carry significant risk to the federal enterprise. BOD 22-01 requires Federal Civilian Executive Branch (FCEB) agencies to remediate identified vulnerabilities by the due date to protect FCEB networks against active threats. See the BOD 22-01 Fact Sheet for more information. Although BOD 22-01 only applies to FCEB agencies, CISA strongly urges all organizations to reduce their exposure to cyberattacks by prioritizing timely remediation of Catalog vulnerabilities as part of their vulnerability management practice. CISA will continue to add vulnerabilities to the catalog that meet the specified criteria.

Researchers and vendors have disclosed a denial-of-service (DoS) vulnerability in HTTP/2 protocol. The vulnerability ( CVE-2023-44487), known as Rapid Reset, has been exploited in the wild in August 2023 through October 2023. CISA recommends organizations that provide HTTP/2 services apply patches when available and consider configuration changes and other mitigations discussed in the references below. For more information on Rapid Reset, see: Cloudflare: HTTP/2 Rapid Reset: deconstructing the record-breaking attack Google: How it works: The novel HTTP/2 ‘Rapid Reset’ DDoS attack AWS: CVE-2023-44487 - HTTP/2 Rapid Reset Attack NGINX: HTTP/2 Rapid Reset Attack Impacting NGINX Products Microsoft Response to Distributed Denial of Service (DDoS) Attacks against HTTP/2 Organizations can take proactive steps to reduce the effects of DoS attacks. See the following guidance for more information: CISA: Understanding and Responding to Distributed Denial-of-Service Attacks CISA: Additional DDoS Guidance for Federal Agencies

Citrix has released security updates to address vulnerabilities affecting multiple products. A malicious cyber actor can exploit one of these vulnerabilities take control of an affected system. CISA encourages users and administrators to review the following Citrix security bulletins and apply the necessary updates: NetScaler ADC and NetScaler Gateway Security Bulletin for CVE-2023-4966 and CVE-2023-4967 Citrix Hypervisor Multiple Security Updates

Microsoft has released updates to address multiple vulnerabilities in Microsoft software. A cyber threat actor can exploit some of these vulnerabilities to take control of an affected system. CISA encourages users and administrators to review Microsoft’s October 2023 Security Update Guide and apply the necessary updates.

Summary Beginning in September 2023, Microsoft was notified by industry partners about a newly identified Distributed Denial-of-Service (DDoS) attack technique being used in the wild targeting HTTP/2 protocol. This vulnerability (CVE-2023-44487) impacts any internet exposed HTTP/2 endpoints. As an industry leader, Microsoft promptly opened an investigation and subsequently began working with industry partners for a coordinated disclosure and mitigation plan.

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