CVE-2026-109163
Description
A flaw was found in Apache HTTP Server's mod_vhost_alias module. A remote attacker could trigger a stack-based buffer overflow by sending a specially crafted HTTP request. This issue leads to a one-byte memory overwrite on the stack, which can crash the server process and result in a Denial of Service (DoS).
Statement
This vulnerability is rated as Moderate impact because successful exploitation terminates worker processes, resulting in a denial of service without leading to remote code execution. In typical Red Hat deployments, dynamic mass virtual hosting using mod_vhost_alias is not enabled by default and requires explicit configuration directives such as VirtualDocumentRoot. Consequently, systems running standard web server configurations without mod_vhost_alias directives are unaffected by this issue.
Mitigation
If dynamic mass virtual hosting is not required, disable the `mod_vhost_alias` module:
1. Comment out the `vhost_alias_module` line in `/etc/httpd/conf.modules.d/00-base.conf` (or the respective configuration file loading the module):
# LoadModule vhost_alias_module modules/mod_vhost_alias.so
2. Restart the Apache HTTP Server service to apply the change:
systemctl restart httpd
Warning: Restarting or reloading the `httpd` service interrupts active connections. Disabling `mod_vhost_alias` will break virtual host resolution for deployments configured with directives such as `VirtualDocumentRoot` or `VirtualScriptAlias`.
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 | 5.9 | N/A | N/A |
| Attack Vector | Network | N/A | N/A |
| Attack Complexity | High | N/A | N/A |
| Privileges Required | None | N/A | N/A |
| User Interaction | None | N/A | N/A |
| Scope | Unchanged | N/A | N/A |
| Confidentiality | None | N/A | N/A |
| Integrity Impact | None | N/A | N/A |
| Availability Impact | High | N/A | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: Modify Memory; 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: Modify Memory; Execute Unauthorized Code or Commands; Bypass Protection Mechanism
Buffer overflows often can be used to execute arbitrary code, which is usually outside the scope of a program's implicit security policy.
Integrity,Confidentiality,Availability,Access Control,Other
Technical Impact: Modify Memory; 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.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
