CVE-2026-63292
Description
A flaw was found in httpd's mod_vhost_alias module. A remote attacker can exploit a stack-based buffer overflow by sending a crafted HTTP request with an excessively large Host header to a server using specific virtual hosting configurations. This issue can lead to arbitrary code execution or cause a Denial of Service (DoS) by crashing the web server.
Mitigation
To mitigate this vulnerability without code modifications, ensure that `LimitRequestFieldSize` remains at or below its default limit of 8190 bytes, or disable the `mod_vhost_alias` module if dynamic virtual hosting is not required.
1. Ensure `LimitRequestFieldSize` is not configured above 8190 in `/etc/httpd/conf/httpd.conf` or `/etc/httpd/conf.d/`:
LimitRequestFieldSize 8190
2. Alternatively, if `mod_vhost_alias` is not needed, disable it by commenting out its loading directive in `/etc/httpd/conf.modules.d/00-base.conf`:
# LoadModule vhost_alias_module modules/mod_vhost_alias.so
3. Validate the configuration syntax and reload the service:
apachectl configtest
systemctl reload httpd
Caveats: Restricting `LimitRequestFieldSize` may reject legitimate requests that carry exceptionally large HTTP headers, returning a 400 Bad Request response. Disabling `mod_vhost_alias` prevents the use of dynamic virtual host directives such as `VirtualDocumentRoot`.
Warning: Reloading or restarting the `httpd` daemon may briefly affect in-flight network connections.
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 | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | High | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | High | N/A | None |
| Integrity Impact | High | N/A | None |
| 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:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
Frequently Asked Questions
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