Several vulnerabilities in NGINX could allow remote code execution

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

A proof-of-concept exploit has been released by DepthFirst. Additionally, a VulnCheck individual reported that CVE-2026-42945 had been exploited in the wild.

Several vulnerabilities have been discovered in NGINX, the most serious of which could allow remote code execution. The details of the vulnerabilities are as follows:

Tactical: Initial access (TA0001):

Technical: Operate a public 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 the attacker-controlled escaped URI data beyond the heap boundary, leading to RCE. (CVE-2026-42945)
• Excessive memory allocation issue in ngx_http_scgi_module and ngx_http_uwsgi_module, state mismatch after incomplete read of upstream status line causes pointer subtraction between buffers. This produces a key length of around 1TB, which crashes the worker process. (CVE-2026-42946)
• A use after free issue in ngx_http_ssl_module, if a TLS connection closes before asynchronous DNS OCSP resolution completes, the context pool is destroyed without canceling the resolver request. The DNS timer will later dereference the freed pointer. (CVE-2026-40701)
• An out-of-bounds read issue in ngx_http_charset_module, a one-by-one error when handling incomplete UTF-8 sequences across proxy buffer bounds corrupts the length state. This calculates a negative source offset, reading 2 bytes before the allocated upstream buffer. (CVE-2026-42934)

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

We recommend that the following actions be taken:

• Apply appropriate updates provided by F5 or other vendors that use this software to vulnerable systems immediately after appropriate testing. (M1051: Update software)
• Backup 7.1: Establish and maintain a vulnerability management process: Establish and maintain a documented vulnerability management process for company assets. Review and update documentation annually or when significant changes within the business occur that could impact this protection.
• 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.
• Backup 7.4: Perform automated application patch management: Perform application updates on enterprise assets with automated patch management on a monthly or more frequent basis.
• Backup 7.5: Perform automated vulnerability scans of internal company assets: Perform automated vulnerability scans of internal company assets on a quarterly or more frequent basis. Perform authenticated and unauthenticated scans using a SCAP-compliant vulnerability scanning tool.
• Backup 7.7: Fix detected vulnerabilities: Remediate detected vulnerabilities in software through processes and tools on a monthly or more frequent basis, depending on the remediation process.
• Backup 12.1: Ensure network infrastructure is up to date: Make sure the network infrastructure is kept up to date. Example implementations include running the latest stable version of the software and/or using currently supported Network as a Service (NaaS) offerings. Review software versions monthly, or more frequently, to verify software support.
• Backup 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 company. Penetration testing program characteristics include scope, such as network, web application, application programming interface (API), hosted services, and physical premises controls; frequency; limitations, such as acceptable hours and excluded types of attacks; contact details; corrective actions, such as how results will be communicated internally; and retrospective requirements.
• Backup 18.2: Perform periodic external penetration tests: Perform periodic external penetration testing based on program requirements, at least annually. External penetration testing should include reconnaissance of the business and environment to detect actionable information. Penetration testing requires specialist skills and experience and should be carried out by a qualified party. The test can be carried out in a transparent box or an opaque box.
• Backup 18.3: Results of corrective penetration tests: Remediate penetration test results based on company policy for scope and priority of remediation.

• Apply the principle of least privilege to all systems and services. Run all software as an unprivileged user (without administrative privileges) to lessen the effects of a successful attack. (M1026: Privileged account management)
• Backup 4.7: Manage default accounts on company assets and software: Manage default accounts on company assets and software, such as root, administrator, and other preconfigured vendor accounts. Example implementations may include: disabling default accounts or rendering them unusable.
• Backup 5.5: Establish and maintain an inventory of service accounts: Establish and maintain an inventory of service accounts. The inventory must at a minimum contain the service owner, review date and purpose. Perform service account reviews to verify that all active accounts are authorized, on a recurring schedule at least quarterly or more frequently.

• Vulnerability scanning is used to find potentially exploitable software vulnerabilities for remediation. (M1016: Vulnerability Analysis)
• Backup 16.13: Perform application penetration testing: Perform application penetration testing. For mission-critical applications, authenticated penetration testing is better suited to detecting business logic vulnerabilities than code analysis and automated security testing. Penetration testing relies on the tester’s ability 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 all Internet-accessible 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)
• Backup 12.2: Establish and maintain a secure network architecture: Establish and maintain a secure network architecture. A secure network architecture must at a minimum take into account segmentation, least privilege and availability.

• Use features to detect and block conditions that could lead to or indicate the occurrence of a software exploit. (M1050: Exploit Protection)
• Backup 10.5: Enable anti-exploitation features: Enable anti-exploitation features on company assets and software where possible, like Microsoft? Data Execution Prevention (DEP), Windows? Defender Exploit Guard (WDEG) or Apple? System Integrity Protection (SIP) and Gatekeeper™.