CVE-2026-93479
Description
A flaw was found in NGINX. An unauthenticated attacker can exploit this vulnerability by sending specially crafted HTTP requests when the map directive uses regular expression (regex) matching and references regex capture variables before referencing the map output variable. This can lead to a heap buffer overflow, which may allow for arbitrary code execution on systems where Address Space Layout Randomization (ASLR) is disabled or bypassed. Additionally, this flaw can cause a denial-of-service (DoS) due to the NGINX worker process restarting.
Security Bulletin
Statement
This vulnerability in NGINX allows a remote, unauthenticated attacker to trigger a heap buffer overflow, leading to a denial of service (DoS). This occurs when the map directive uses regex matching and references regex capture variables before the map output variable. While arbitrary code execution is a theoretical risk, it is significantly reduced on Red Hat systems where Address Space Layout Randomization (ASLR) is enabled by default.
CVE-2026-93479 is a regression caused by the fix for CVE-2026-42533.
Mitigation
To mitigate this vulnerability, do not use unnamed captures. Use named captures instead and only use them in the same block with the regex match. Red Hat recommends updating nginx to the latest version when a fix is available.
According to F5, the following versions contain the fix: 1.31.7, 1.30.6
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | N/A | 8.1 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | High |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | Low | N/A | High |
| Integrity Impact | Low | N/A | High |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Red Hat CVSS v3 Score Explanation
Adjusted from upstream C:H/I:H/A:H (8.1) to C:L/I:L/A:H (7.0). C:L/I:L: code execution requires ASLR disabled or bypassed — ASLR is enabled by default on all RHEL systems, making RCE unlikely; bounded to low. A:H: sustained crafted requests can keep crashing nginx worker processes, causing meaningful service disruption despite auto-restart. Aligned with alias CVE-2026-42533.
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Crash, Exit, or Restart; DoS: Resource Consumption (CPU); DoS: Resource Consumption (Memory)
Buffer overflows generally lead to crashes. Other attacks leading to lack of availability are possible, including putting the program into an infinite loop.
Integrity,Confidentiality,Availability,Access Control
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Modify Memory
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy. Besides important user data, heap-based overflows can be used to overwrite function pointers that may be living in memory, pointing it to the attacker's code. Even in applications that do not explicitly use function pointers, the run-time will usually leave many in memory. For example, object methods in C++ are generally implemented using function pointers. Even in C programs, there is often a global offset table used by the underlying runtime.
Integrity,Confidentiality,Availability,Access Control,Other
Technical Impact: Execute Unauthorized Code or Commands; Bypass Protection Mechanism; Other
When the consequence is arbitrary code execution, this can often be used to subvert any other security service.
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