CVE-2026-42055
Description
A flaw was found in NGINX. When NGINX is configured to proxy HTTP/2 traffic using the ngx_http_proxy_v2_module or ngx_http_grpc_module with specific settings, a remote, unauthenticated attacker can send specially crafted large headers. This can trigger a heap-based buffer overflow, leading to a restart of the NGINX worker process and a Denial of Service (DoS). Under certain conditions, such as when Address Space Layout Randomization (ASLR) is disabled or bypassed, this vulnerability could also allow for arbitrary code execution.
Statement
This issue is classified as Important severity primarily because: Conditions for Exploitation: A remote, unauthenticated attacker can only exploit this if NGINX is explicitly configured to proxy HTTP/2 traffic using the ngx_http_proxy_v2_module or ngx_http_grpc_module.
Impact Limitations: While the flaw reliably causes a Denial of Service (worker restart), achieving arbitrary code execution is highly complex in modern environments as it requires the attacker to bypass or disable Address Space Layout Randomization (ASLR)
Mitigation
To mitigate this vulnerability, ensure that the `ignore_invalid_headers` directive is set to `on` in your NGINX configuration, or reduce the size specified by the `large_client_header_buffers` directive to 2 megabytes or less. These changes require an NGINX service reload or restart to take effect. Reloading the NGINX service is generally safe, but a restart will briefly interrupt service.
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 8.1 | 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 | High | N/A | High |
| Integrity Impact | High | 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:H/I:H/A:H
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Integrity,Availability,Confidentiality
Technical Impact: DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands; Read Memory; Modify Memory
If the incorrect calculation is used in the context of memory allocation, then the software may create a buffer that is smaller or larger than expected. If the allocated buffer is smaller than expected, this could lead to an out-of-bounds read or write (CWE-119), possibly causing a crash, allowing arbitrary code execution, or exposing sensitive data.
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