CVE-2016-4979
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…
Does this matter?
EPSS puts the probability of exploitation in the next 30 days at 18.8%, higher than 97% of all known CVEs. Patch or mitigate before the next change window.
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
- 7.5 HIGHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
- EPSS
- 18.80% probability · 97th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-284
- Affected
- apache/http server
- Source
- secalert@redhat.com
EPSS 18.8% since 26 October 2026; no change recorded yet. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- http://httpd.apache.org/security/vulnerabilities_24.htmlPatch, Vendor 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%3E
- https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/re3d27b6250aa8548b8845d314bb8a350b3df326cacbbfdfe4d455234%40%3Ccvs.httpd.apache.org%3E
- https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E
- https://security.gentoo.org/glsa/201610-02
- https://security.netapp.com/advisory/ntap-20180601-0001/
- http://httpd.apache.org/security/vulnerabilities_24.htmlPatch, Vendor 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
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.