httpd: X509 client certificate authentication bypass using HTTP/2
Published Jul 6, 2016
9.1
CRITICALCVSS 3.0
EPSS 18.80%
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.
Affected products
No data.
- 2.4.18
- 2.4.19
- 2.4.20
No data.
Red Hat Software Collections for Red Hat Enterprise Linux 6
httpd24-httpd-0:2.4.18-11.el6
Fixed · RHSA-2016:1420
Red Hat Software Collections for Red Hat Enterprise Linux 6.6 EUS
httpd24-httpd-0:2.4.18-11.el6
Fixed · RHSA-2016:1420
Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUS
httpd24-httpd-0:2.4.18-11.el6
Fixed · RHSA-2016:1420
Red Hat Software Collections for Red Hat Enterprise Linux 7
httpd24-httpd-0:2.4.18-11.el7
Fixed · RHSA-2016:1420
Red Hat Software Collections for Red Hat Enterprise Linux 7.1 EUS
httpd24-httpd-0:2.4.18-11.el7
Fixed · RHSA-2016:1420
Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUS
httpd24-httpd-0:2.4.18-11.el7
Fixed · RHSA-2016:1420
Red Hat Directory Server 8
httpd
Not affected
Red Hat Enterprise Linux 5
httpd
Not affected
Red Hat Enterprise Linux 6
httpd
Not affected
Red Hat Enterprise Linux 7
httpd
Not affected
Red Hat JBoss Core Services
jbcs-httpd24-httpd
Not affected
Red Hat JBoss Enterprise Application Platform 5
httpd
Not affected
Red Hat JBoss Enterprise Application Platform 6
httpd
Not affected
Red Hat JBoss Enterprise Application Platform 6
httpd22
Not affected
Red Hat JBoss Enterprise Web Server 1
httpd
Not affected
Red Hat JBoss Enterprise Web Server 2
httpd
Not affected
Red Hat JBoss Enterprise Web Server 3
httpd
Not affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Software Collections for Red Hat Enterprise Linux 6 | httpd24-httpd-0:2.4.18-11.el6 | Fixed | RHSA-2016:1420 |
| Red Hat Software Collections for Red Hat Enterprise Linux 6.6 EUS | httpd24-httpd-0:2.4.18-11.el6 | Fixed | RHSA-2016:1420 |
| Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUS | httpd24-httpd-0:2.4.18-11.el6 | Fixed | RHSA-2016:1420 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7 | httpd24-httpd-0:2.4.18-11.el7 | Fixed | RHSA-2016:1420 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7.1 EUS | httpd24-httpd-0:2.4.18-11.el7 | Fixed | RHSA-2016:1420 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUS | httpd24-httpd-0:2.4.18-11.el7 | Fixed | RHSA-2016:1420 |
| Red Hat Directory Server 8 | httpd | Not affected | n/a |
| Red Hat Enterprise Linux 5 | httpd | Not affected | n/a |
| Red Hat Enterprise Linux 6 | httpd | Not affected | n/a |
| Red Hat Enterprise Linux 7 | httpd | Not affected | n/a |
| Red Hat JBoss Core Services | jbcs-httpd24-httpd | Not affected | n/a |
| Red Hat JBoss Enterprise Application Platform 5 | httpd | Not affected | n/a |
| Red Hat JBoss Enterprise Application Platform 6 | httpd | Not affected | n/a |
| Red Hat JBoss Enterprise Application Platform 6 | httpd22 | Not affected | n/a |
| Red Hat JBoss Enterprise Web Server 1 | httpd | Not affected | n/a |
| Red Hat JBoss Enterprise Web Server 2 | httpd | Not affected | n/a |
| Red Hat JBoss Enterprise Web Server 3 | httpd | Not affected | n/a |
No package ranges for this CVE.
Remediation
No remediation recorded yet.
Metrics
No CVSS v4.0 score for this CVE.
No CVSS v3.1 score for this CVE.
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
1 other source (Red Hat) ▾
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
AV:N/AC:L/Au:N/C:N/I:P/A:N
This CVE is not in the KEV list.
No CISA SSVC assessment for this CVE yet.
Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 1, 2026.
Score over time
2022–2026- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Percentile over time
- EPSS v2
- EPSS v3
- EPSS v4
- EPSS v5
Table of values (42 key points)
Flat stretches are collapsed; showing up to 120 newest points.
| Date | Score | Percentile | Model |
|---|---|---|---|
| Oct 1, 2026 | 18.80% (0.18802) | 97.20th | v5 (v2026.06.15) |
| Jun 15, 2026 | 18.80% (0.18802) | 96.91th | v5 (v2026.06.15) |
| Jun 9, 2026 | 27.57% (0.27575) | 96.54th | v4 (v2025.03.14) |
| Mar 8, 2026 | 17.36% (0.17360) | 94.94th | v4 (v2025.03.14) |
| Mar 4, 2026 | 32.73% (0.32726) | 96.78th | v4 (v2025.03.14) |
| Mar 1, 2026 | 29.79% (0.29785) | 96.56th | v4 (v2025.03.14) |
| Feb 4, 2026 | 32.73% (0.32726) | 96.75th | v4 (v2025.03.14) |
| Feb 1, 2026 | 29.79% (0.29785) | 96.54th | v4 (v2025.03.14) |
| Jan 4, 2026 | 32.73% (0.32726) | 96.71th | v4 (v2025.03.14) |
| Jan 1, 2026 | 29.79% (0.29785) | 96.51th | v4 (v2025.03.14) |
| Dec 4, 2025 | 32.73% (0.32726) | 96.68th | v4 (v2025.03.14) |
| Dec 3, 2025 | 29.79% (0.29785) | 96.47th | v4 (v2025.03.14) |
| Dec 1, 2025 | 14.46% (0.14462) | 94.21th | v4 (v2025.03.14) |
| Nov 4, 2025 | 16.57% (0.16569) | 94.63th | v4 (v2025.03.14) |
| Nov 1, 2025 | 14.46% (0.14462) | 94.19th | v4 (v2025.03.14) |
| Oct 4, 2025 | 16.57% (0.16569) | 94.66th | v4 (v2025.03.14) |
| Oct 1, 2025 | 14.46% (0.14462) | 94.24th | v4 (v2025.03.14) |
| Sep 4, 2025 | 16.91% (0.16906) | 94.72th | v4 (v2025.03.14) |
| Sep 1, 2025 | 8.67% (0.08671) | 92.16th | v4 (v2025.03.14) |
| Aug 29, 2025 | 16.91% (0.16906) | 94.70th | v4 (v2025.03.14) |
| Aug 28, 2025 | 8.67% (0.08671) | 92.08th | v4 (v2025.03.14) |
| Aug 23, 2025 | 32.93% (0.32930) | 96.73th | v4 (v2025.03.14) |
| Aug 4, 2025 | 49.68% (0.49683) | 97.71th | v4 (v2025.03.14) |
| Aug 1, 2025 | 32.93% (0.32930) | 96.75th | v4 (v2025.03.14) |
| Jul 30, 2025 | 49.68% (0.49683) | 97.71th | v4 (v2025.03.14) |
| Jul 4, 2025 | 44.54% (0.44542) | 97.42th | v4 (v2025.03.14) |
| Jul 1, 2025 | 40.64% (0.40641) | 97.22th | v4 (v2025.03.14) |
| Jun 4, 2025 | 44.54% (0.44542) | 97.39th | v4 (v2025.03.14) |
| Jun 1, 2025 | 40.64% (0.40641) | 97.20th | v4 (v2025.03.14) |
| May 4, 2025 | 44.54% (0.44542) | 97.38th | v4 (v2025.03.14) |
| May 1, 2025 | 40.64% (0.40641) | 97.17th | v4 (v2025.03.14) |
| Mar 30, 2025 | 44.54% (0.44542) | 97.30th | v4 (v2025.03.14) |
| Mar 29, 2025 | 51.08% (0.51078) | 96.88th | v4 (v2025.03.14) |
| Mar 23, 2025 | 44.54% (0.44542) | 97.18th | v4 (v2025.03.14) |
| Mar 19, 2025 | 32.52% (0.32524) | 96.31th | v4 (v2025.03.14) |
| Mar 17, 2025 | 37.31% (0.37311) | 96.82th | v4 (v2025.03.14) |
| Dec 12, 2024 | 0.21% (0.00211) | 59.96th | v3 (v2023.03.01) |
| Jun 13, 2024 | 0.21% (0.00211) | 59.20th | v3 (v2023.03.01) |
| Mar 7, 2023 | 0.21% (0.00211) | 57.19th | v3 (v2023.03.01) |
| Mar 6, 2023 | 7.34% (0.07344) | 92.59th | v2 (v2022.01.01) |
| Apr 1, 2022 | 7.34% (0.07344) | 91.87th | v2 (v2022.01.01) |
| Feb 4, 2022 | 7.34% (0.07344) | 80.64th | v2 (v2022.01.01) |
References (30)
- http://httpd.apache.org/security/vulnerabilities_24.html x_refsource_CONFIRMPatchVendor Advisory
- http://httpd.apache.org/security/vulnerabilities_24.html#2.4.23
- http://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html x_refsource_MISC
- http://seclists.org/fulldisclosure/2016/Jul/11 mailing-listx_refsource_FULLDISC
- http://www.apache.org/dist/httpd/CHANGES_2.4 x_refsource_CONFIRM
- http://www.openwall.com/lists/oss-security/2016/07/05/5 mailing-listx_refsource_MLIST
- http://www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html x_refsource_CONFIRM
- http://www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html x_refsource_CONFIRM
- http://www.securityfocus.com/bid/91566 vdb-entryx_refsource_BID
- http://www.securitytracker.com/id/1036225 vdb-entryx_refsource_SECTRACK
- https://access.redhat.com/errata/RHSA-2016:1420 vendor-advisoryx_refsource_REDHAT
- https://access.redhat.com/security/cve/CVE-2016-4979 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=1352476 Issue Tracking
- https://github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2 x_refsource_CONFIRM
- https://lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/re3d27b6250aa8548b8845d314bb8a350b3df326cacbbfdfe4d455234%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://lists.apache.org/thread.html/rf6449464fd8b7437704c55f88361b66f12d5b5f90bcce66af4be4ba9%40%3Ccvs.httpd.apache.org%3E mailing-listx_refsource_MLIST
- https://nvd.nist.gov/vuln/detail/CVE-2016-4979
- https://security.gentoo.org/glsa/201610-02 vendor-advisoryx_refsource_GENTOO
- https://security.netapp.com/advisory/ntap-20180601-0001/ x_refsource_CONFIRM
- https://www.cve.org/CVERecord?id=CVE-2016-4979
Change history (0)
No recorded changes yet.