Multiple Vulnerabilities in NGINX Could Allow for Remote Code Execution

Multiple vulnerabilities have been discovered in NGINX, the most severe of which could allow for remote code execution. NGINX is a software used for web serving, reverse proxying, caching, and load balancing. Successful exploitation of the most severe of these vulnerabilities may allow an unauthenticated threat actor to crash vulnerable NGINX worker processes by sending crafted HTTP requests. Additionally, for systems with Address Space Layout Randomization (ASLR) disabled, exploitation may result in remote code execution. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have less rights on the system could be less impacted than those who operate with administrative user rights.

A proof-of concept exploit has been published by DepthFirst. In addition, an individual at VulnCheck has reported that CVE-2026-42945 has been exploited in the wild.

Multiple vulnerabilities have been discovered in NGINX, the most severe of which could allow for remote code execution. Details of the vulnerabilities are as follows:

Tactic: Initial Access (TA0001):

Technique: Exploit Public-Facing Application (T1190):

• A heap buffer overflow issue in ngx_http_rewrite_module, an unpropagated is_args flag during a rewrite and set sequence causes an undersized buffer allocation. The copy phase then writes attacker-controlled escaped URI data past the heap boundary, leading to RCE. (CVE-2026-42945)
• An excessive memory allocation issue in ngx_http_scgi_module and ngx_http_uwsgi_module, a state mismatch after an incomplete upstream status line read causes a cross-buffer pointer subtraction. This produces a ~1 TB key length, crashing the worker process. (CVE-2026-42946)
• A use after free issue in ngx_http_ssl_module, if a TLS connection closes before asynchronous OCSP DNS resolution completes, the context pool is destroyed without cancelling the resolver request. The DNS timer later dereferences the freed pointer. (CVE-2026-40701)
• An out-of-bounds read issue in ngx_http_charset_module, an off-by-one error when handling incomplete UTF-8 sequences across proxy buffer boundaries corrupts the length state. This computes a negative source offset, reading 2 bytes before the allocated upstream buffer. (CVE-2026-42934)

Successful exploitation of the most severe of these vulnerabilities may allow an unauthenticated threat actor to crash vulnerable NGINX worker processes by sending crafted HTTP requests. Additionally, for systems with Address Space Layout Randomization (ASLR) disabled, exploitation may result in remote code execution. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have less rights on the system could be less impacted than those who operate with administrative user rights.

We recommend the following actions be taken:

• Apply appropriate updates provided by F5 or other vendors which use this software to vulnerable systems immediately after appropriate testing. (M1051: Update Software)
• Safeguard 7.1 : Establish and Maintain a Vulnerability Management Process: Establish and maintain a documented vulnerability management process for enterprise assets. Review and update documentation annually, or when significant enterprise changes occur that could impact this Safeguard.
• Safeguard 7.2: Establish and Maintain a Remediation Process: Establish and maintain a risk-based remediation strategy documented in a remediation process, with monthly, or more frequent, reviews.
• Safeguard 7.4: Perform Automated Application Patch Management: Perform application updates on enterprise assets through automated patch management on a monthly, or more frequent, basis.
• Safeguard 7.5 : Perform Automated Vulnerability Scans of Internal Enterprise Assets: Perform automated vulnerability scans of internal enterprise assets on a quarterly, or more frequent, basis. Conduct both authenticated and unauthenticated scans, using a SCAP-compliant vulnerability scanning tool.
• Safeguard 7.7: Remediate Detected Vulnerabilities: Remediate detected vulnerabilities in software through processes and tooling on a monthly, or more frequent, basis, based on the remediation process.
• Safeguard 12.1: Ensure Network Infrastructure is Up-to-Date: Ensure network infrastructure is kept up-to-date. Example implementations include running the latest stable release of software and/or using currently supported network-as-a-service (NaaS) offerings. Review software versions monthly, or more frequently, to verify software support.
• Safeguard 18.1: Establish and Maintain a Penetration Testing Program: Establish and maintain a penetration testing program appropriate to the size, complexity, and maturity of the enterprise. Penetration testing program characteristics include scope, such as network, web application, Application Programming Interface (API), hosted services, and physical premise controls; frequency; limitations, such as acceptable hours, and excluded attack types; point of contact information; remediation, such as how findings will be routed internally; and retrospective requirements.
• Safeguard 18.2: Perform Periodic External Penetration Tests: Perform periodic external penetration tests based on program requirements, no less than annually. External penetration testing must include enterprise and environmental reconnaissance to detect exploitable information. Penetration testing requires specialized skills and experience and must be conducted through a qualified party. The testing may be clear box or opaque box.
• Safeguard 18.3: Remediate Penetration Test Findings: Remediate penetration test findings based on the enterprise’s policy for remediation scope and prioritization.

• Apply the Principle of Least Privilege to all systems and services. Run all software as a non-privileged user (one without administrative privileges) to diminish the effects of a successful attack. (M1026: Privileged Account Management)
• Safeguard 4.7: Manage Default Accounts on Enterprise Assets and Software: Manage default accounts on enterprise assets and software, such as root, administrator, and other pre-configured vendor accounts. Example implementations can include: disabling default accounts or making them unusable.
• Safeguard 5.5: Establish and Maintain an Inventory of Service Accounts: Establish and maintain an inventory of service accounts. The inventory, at a minimum, must contain department owner, review date, and purpose. Perform service account reviews to validate that all active accounts are authorized, on a recurring schedule at a minimum quarterly, or more frequently.

• Vulnerability scanning is used to find potentially exploitable software vulnerabilities to remediate them. (M1016: Vulnerability Scanning)
• Safeguard 16.13: Conduct Application Penetration Testing: Conduct application penetration testing. For critical applications, authenticated penetration testing is better suited to finding business logic vulnerabilities than code scanning and automated security testing. Penetration testing relies on the skill of the tester to manually manipulate an application as an authenticated and unauthenticated user.

• Architect sections of the network to isolate critical systems, functions, or resources. Use physical and logical segmentation to prevent access to potentially sensitive systems and information. Use a DMZ to contain any internet-facing services that should not be exposed from the internal network. Configure separate virtual private cloud (VPC) instances to isolate critical cloud systems. (M1030: Network Segmentation)
• Safeguard 12.2: Establish and Maintain a Secure Network Architecture: Establish and maintain a secure network architecture. A secure network architecture must address segmentation, least privilege, and availability, at a minimum.

• Use capabilities to detect and block conditions that may lead to or be indicative of a software exploit occurring. (M1050: Exploit Protection)
• Safeguard 10.5: Enable Anti-Exploitation Features: Enable anti-exploitation features on enterprise assets and software, where possible, such as Microsoft? Data Execution Prevention (DEP), Windows? Defender Exploit Guard (WDEG), or Apple? System Integrity Protection (SIP) and Gatekeeper™.