CVE-2019-11043
Description
From CVE.org
In PHP versions 7.1.x below 7.1.33, 7.2.x below 7.2.24 and 7.3.x below 7.3.11 in certain configurations of FPM setup it is possible to cause FPM module to write past allocated buffers into the space reserved for FCGI protocol data, thus opening the possibility of remote code execution.
Statement
This issue only affects instances running php-fpm under nginx server software as environment paths and parameters are handled by different code pieces depending on the server php-fpm is running under. The code where this issue is found is used exclusively when php-fpm detects the request came through an nginx server.
Red Hat Product Security team rated this issue as having a Critical security impact as an attacker may take advantage from the existing bug to cause Remote Code Execution on network exposed software.
Mitigation
1) Check your nginx configuration files, specially the ones related to php-fpm for presence of pattern bellow on fastcgi_split_path_info regex and PATH_INFO parameter:
fastcgi_split_path_info ^(.+?\.php)(/.*)$;
fastcgi_param PATH_INFO $fastcgi_path_info;
2) If fastcgi_split_path_info regex matches with the one above, for each fastcgi_param PATH_INFO entry perform the following change:
fastcgi_param PATH_INFO $fastcgi_path_info if_not_empty;
This step will allow you to safely continue using PATH_INFO parameter while the patch is not applied.
3) Restart your nginx instance:
systemctl restart nginx
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 | 9.8 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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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