Description
The Apache HTTP Server 2.4.18 through 2.4.20, when mod_http2 and mod_ssl are enabled, does not properly recognize the "SSLVerifyClient require" directive for HTTP/2 request authorization, which allows remote attackers to bypass intended access restrictions by leveraging the ability to send multiple requests over a single connection and aborting a renegotiation.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | apache2 | 2.4.23-1 | — |
| Debian 13 | apache2 | 2.4.23-1 | — |
| Debian 12 | apache2 | 2.4.23-1 | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| RHEL 2 | httpd24-httpd +5 | 2.4.18-11.el6 | RHSA-2016:1420 |
| RHEL 2 | httpd24-mod_ssl +1 | 1:2.4.18-11.el6 | RHSA-2016:1420 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | apache2 | 2.4.23-4.1 | openSUSE-SU-2024:10268-1 |
Advisories 2
- RHSA-2016:1420 Red Hat Security Advisory: httpd24-httpd security update Red Hat Security Advisories (RHSA) · Sep 21, 2026
- openSUSE-SU-2024:10268-1 apache2-2.4.23-4.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026
References
- RHSA-2016:1420 vendor-advisory
- http://httpd.apache.org/security/vulnerabilities_24.html
- GLSA-201610-02 vendor-advisory
- 20160706 CVE-2016-4979: HTTPD webserver - X509 Client certificate based authentication can be bypassed when HTTP/2 is used [vs] mailing-list
- http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
- http://www.apache.org/dist/httpd/CHANGES_2.4
- 91566 vdb-entry
- http://www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html
- 1036225 vdb-entry
- [oss-security] 20160705 CVE-2016-4979: HTTPD webserver - X509 Client certificate based authentication can be bypassed when HTTP/2 is used [vs] mailing-list
- https://github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2
- http://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html
- https://security.netapp.com/advisory/ntap-20180601-0001/
- [httpd-cvs] 20190815 svn commit: r1048743 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/vulnerabilities-httpd.xml security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabilit mailing-list
- [httpd-cvs] 20190815 svn commit: r1048742 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/vulnerabilities-httpd.xml security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabilit mailing-list
- [httpd-cvs] 20200401 svn commit: r1058586 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/vulnerabilities-httpd.xml security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabilit mailing-list
- [httpd-cvs] 20200401 svn commit: r1058587 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/vulnerabilities-httpd.xml security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabilit mailing-list
- [httpd-cvs] 20210330 svn commit: r1073139 [1/13] - in /websites/staging/httpd/trunk/content: ./ security/json/ mailing-list
- [httpd-cvs] 20210330 svn commit: r1073140 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/cvejsontohtml.py security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabilities_24.ht mailing-list
- [httpd-cvs] 20210330 svn commit: r1888194 [10/13] - /httpd/site/trunk/content/security/json/ mailing-list
- [httpd-cvs] 20210330 svn commit: r1073139 [10/13] - in /websites/staging/httpd/trunk/content: ./ security/json/ mailing-list
- [httpd-cvs] 20210330 svn commit: r1073149 [1/13] - in /websites/staging/httpd/trunk/content: ./ security/ security/json/ mailing-list
- [httpd-cvs] 20210330 svn commit: r1073146 [3/3] - in /websites/staging/httpd/trunk/content: ./ security/cvejsontohtml.py security/vulnerabilities-httpd.xml security/vulnerabilities_22.html security/vulnerabilities_24.html mailing-list
- [httpd-cvs] 20210330 svn commit: r1073149 [10/13] - in /websites/staging/httpd/trunk/content: ./ security/ security/json/ mailing-list
- [httpd-cvs] 20210606 svn commit: r1075470 [4/4] - in /websites/staging/httpd/trunk/content: ./ security/json/CVE-2020-13938.json security/vulnerabilities_13.html security/vulnerabilities_20.html security/vulnerabilities_22.html security/vulnerabiliti mailing-list