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Vulnerability record · CVE-2016-4979 · published 6 July 2016

CVE-2016-4979: Apache http server improper access control vulnerability

Apache · Http Server

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.

7.5 CVSS 3.0 High EPSS 19% · top 2.8% CWE-284 · Improper access control
7.5CVSS 3.0 base score, v2 5.0
19%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
50References
17 Jun 2026Last modified by NVD

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.

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://httpd.apache.org/security/vulnerabilities_24.html PatchVendor Advisory
http://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html
http://seclists.org/fulldisclosure/2016/Jul/11
http://www.apache.org/dist/httpd/CHANGES_2.4
http://www.openwall.com/lists/oss-security/2016/07/05/5
http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
http://www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html
http://www.securityfocus.com/bid/91566
http://www.securitytracker.com/id/1036225
https://access.redhat.com/errata/RHSA-2016:1420
https://github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2
https://lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%
https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%
https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/re3d27b6250aa8548b8845d314bb8a350b3df326cacbbfdfe4d455234%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org
https://security.gentoo.org/glsa/201610-02
https://security.netapp.com/advisory/ntap-20180601-0001/
http://httpd.apache.org/security/vulnerabilities_24.html PatchVendor Advisory
http://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html
http://seclists.org/fulldisclosure/2016/Jul/11
http://www.apache.org/dist/httpd/CHANGES_2.4
http://www.openwall.com/lists/oss-security/2016/07/05/5
http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
http://www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html
http://www.securityfocus.com/bid/91566
http://www.securitytracker.com/id/1036225
https://access.redhat.com/errata/RHSA-2016:1420
https://github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2
https://lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%
https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%
https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org
https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org

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Source: NIST National Vulnerability Database (record CVE-2016-4979), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.