CVE-2017-9798
Description
A use-after-free flaw was found in the way httpd handled invalid and previously unregistered HTTP methods specified in the Limit directive used in an .htaccess file. A remote attacker could possibly use this flaw to disclose portions of the server memory, or cause httpd child process to crash.
Statement
This issue affects the versions of httpd as shipped with Red Hat Enterprise Linux 5, 6, and 7. This issue affects the versions of httpd24-httpd as shipped with Red Hat Software Collections. Product Security has rated this issue as having Moderate security impact.
In order to be vulnerable, .htaccess files need to contain an invalid or not globally registered HTTP method in a "Limit" directive.
Mitigation
This issue can be mitigated by configuring httpd to disallow the use of the "Limit" configuration directive in .htaccess files. The set of directives that can be used in .htaccess files is configured using the "AllowOverride" directive. Refer to Red Hat Bugzilla bug 1490344 for further details:
https://bugzilla.redhat.com/show_bug.cgi?id=1490344#c18
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 | 5.9 | 7.5 | 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 | None | None | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory
The use of previously freed memory may corrupt valid data, if the memory area in question has been allocated and used properly elsewhere.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
If chunk consolidation occurs after the use of previously freed data, the process may crash when invalid data is used as chunk information.
Confidentiality
Technical Impact: Read Memory
Read operations on freed memory can sometimes leak sensitive information instead of causing a crash
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
If malicious data is entered before chunk consolidation can take place, it may be possible to take advantage of a write-what-where primitive to execute arbitrary code. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.
Acknowledgements
Red Hat would like to thank Hanno Böck for reporting this issue.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
