CVE-2026-63686
Description
A flaw was found in the mod_xml2enc module of the Apache HTTP Server. An untrusted backend server can cause a Denial of Service (DoS) by returning a crafted response with a character set whose conversion partially succeeds and then fails. Processing this response triggers an invalid memory access (null pointer dereference), causing the server process to crash.
Mitigation
If proxy character set transcoding is not required, disable the mod_xml2enc module by commenting out its configuration directive.
1. Edit the module configuration file (typically located under `/etc/httpd/conf.modules.d/`) and comment out the loading directive:
# LoadModule xml2enc_module modules/mod_xml2enc.so
2. Verify the configuration syntax:
httpd -t
3. Reload the Apache HTTP Server to apply changes:
systemctl reload httpd
Caveats: Disabling mod_xml2enc will break modules that depend on XML or HTML character set conversion, such as mod_proxy_html. If this module is required, restrict proxy rules so httpd communicates only with trusted upstream backends.
Warning: Reloading or restarting the httpd service may cause a brief interruption to active 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 | 7.5 | N/A | 7.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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)
Availability
Technical Impact: DoS: Crash, Exit, or Restart
NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation.
Integrity,Confidentiality
Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory
In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution.
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