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…
Noroxi assessment
Priority: Monitor (action score 36/100)
- The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
- Probability of exploitation in the next 30 days: 18.8% (FIRST EPSS); higher than 97.3% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- Fixed version: apache2 (Debian:12) 2.4.23-1; httpd24-httpd (Red Hat:rhel_software_collections:2::el6) 0:2.4.18-11.el6; httpd24-httpd-debuginfo (Red Hat:rhel_software_collections:2::el6) 0:2.4.18-11.el6.
Low priority for now. Upgrade to apache2 (Debian:12) 2.4.23-1; httpd24-httpd (Red Hat:rhel_software_collections:2::el6) 0:2.4.18-11.el6; httpd24-httpd-debuginfo (Red Hat:rhel_software_collections:2::el6) 0:2.4.18-11.el6 or later.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
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.
- Published
- Jul 6, 2016
- Updated
- Jun 16, 2026
- EPSS
- 18.8% · 97th percentile
- CWE
- CWE-284
Report tools
Action score
36
Low priority for now.
- CVSS
- 30 / 40 · 7.5 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 6 / 30 · 18.8%
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- No public exploit code on record
- A fix has been released
If any of these changes, we'll tell you in the daily email digest.
Is Apache HTTP Server on your server exposed to the internet?Run a port scan
Is your version affected? Check itNoroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| apache | http server | cpe:2.3:a:apache:http_server |
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Run a port scanAffected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- apache http server2.4.18
- apache http server2.4.19
- apache http server2.4.20
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Debian:12 | apache2 | before 2.4.23-1 | 2.4.23-1 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-httpd | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-httpd-debuginfo | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-httpd-devel | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-httpd-manual | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-httpd-tools | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-mod_ldap | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-mod_proxy_html | before 1:2.4.18-11.el6 | 1:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-mod_session | before 0:2.4.18-11.el6 | 0:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el6 | httpd24-mod_ssl | before 1:2.4.18-11.el6 | 1:2.4.18-11.el6 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-httpd | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-httpd-debuginfo | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-httpd-devel | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-httpd-manual | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-httpd-tools | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-mod_ldap | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-mod_proxy_html | before 1:2.4.18-11.el7 | 1:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-mod_session | before 0:2.4.18-11.el7 | 0:2.4.18-11.el7 |
| Red Hat:rhel_software_collections:2::el7 | httpd24-mod_ssl | before 1:2.4.18-11.el7 | 1:2.4.18-11.el7 |
Same product
apache: all recordsOther highest-scoring records for the same primary product.
- CVE-2021-42013Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)KEV99Now
- CVE-2021-41773Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49KEV99Now
- CVE-2024-38475Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path.KEV96Now
Published before and after this one in the same product
- ← EarlierCVE-2015-3185Jul 20, 2015 · The ap_some_auth_required function in server/request.c in the Apache HTTP Server 2.4.x before 2.4.14 does not consider that a Require…22Monitor
- ← EarlierCVE-2016-1546Jul 6, 2016 · The Apache HTTP Server 2.4.17 and 2.4.18, when mod_http2 is enabled, does not limit the number of simultaneous stream workers for a single…28Monitor
- Later →CVE-2016-5387Jul 18, 2016 · The Apache HTTP Server through 2.4.23 follows RFC 3875 section 4.1.18 and therefore does not protect applications from the presence of…49Plan
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| debian:apache2 | 2.4.23-1 · Debian:12 | Package registry (OSV) |
| red hat:httpd24-httpd | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-httpd-debuginfo | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-httpd-devel | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-httpd-manual | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-httpd-tools | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-mod_ldap | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-mod_proxy_html | 1:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-mod_session | 0:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
| red hat:httpd24-mod_ssl | 1:2.4.18-11.el6 · Red Hat:rhel_software_collections:2::el6 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Not on record for this CVE: EPSS history · researcher credit · variant or chain candidate · public bounty program.
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- none
- Integrity
- high · data or configuration can be modified
- Availability
- none
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- None
- Integrity impact
- High
- Availability impact
- None
Weakness class (CWE)
CWE-284 · Improper Access ControlCVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Embedding Scripts within ScriptsCAPEC-19likelihood: High · High
- Malicious Logic InsertionCAPEC-441likelihood: Medium · High
- Modification of Windows Service ConfigurationCAPEC-478likelihood: Low · High
- Malicious Root CertificateCAPEC-479likelihood: Low · Low
- Intent SpoofCAPEC-502
- WebView ExposureCAPEC-503
- Data Injected During ConfigurationCAPEC-536likelihood: Low · High
- Incomplete Data Deletion in a Multi-Tenant EnvironmentCAPEC-546likelihood: Low · Medium
ATT&CK techniques
- RootkitT1014
- Obfuscated Files or Information: Embedded PayloadsT1027.009
- Boot or Logon Initialization ScriptsT1037
- Taint shared contentT1080
- Server Software Component: Terminal Services DLLT1505.005
- Pre-OS Boot:BootkitT1542.003
- Create or Modify System ProcessT1543
- Create or Modify System Process: Launch AgentT1543.001
- Create or Modify System Process:Windows ServiceT1543.003
- Create or Modify System Process: Launch DaemonT1543.004
- Event Triggered Execution:Change Default File AssociationT1546.001
- Event Triggered Execution:.bash_profile and .bashrcT1546.004
- Event Triggered Execution: Accessibility FeaturesT1546.008
- Event Triggered Execution: Installer PackagesT1546.016
- Boot or Logon Autostart ExecutionT1547
- Boot or Logon Autostart Execution:Kernel Modules and ExtensionsT1547.006
Change log (1)
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
Show all references (19 more)Show less
- seclists.org/fulldisclosure/2016/Jul/11
- www.apache.org/dist/httpd/CHANGES_2.4
- www.openwall.com/lists/oss-security/2016/07/05/5
- www.oracle.com/technetwork/security-advisory/cpuoct2016-2881722.html
- www.oracle.com/technetwork/topics/security/bulletinoct2016-3090566.html
- www.securityfocus.com/bid/91566
- www.securitytracker.com/id/1036225
- access.redhat.com/errata/RHSA-2016:1420
- github.com/apache/httpd/commit/2d0e4eff04ea963128a41faaef21f987272e05a2
- lists.apache.org/thread.html/56c2e7cc9deb1c12a843d0dc251ea7fd3e7e80293cde02fcd65286ba%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/84a3714f0878781f6ed84473d1a503d2cc382277e100450209231830%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/r04e89e873d54116a0635ef2f7061c15acc5ed27ef7500997beb65d6f%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/r76142b8c5119df2178be7c2dba88fde552eedeec37ea993dfce68d1d%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/r9f93cf6dde308d42a9c807784e8102600d0397f5f834890708bf6920%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/rb14daf9cc4e28d18cdc15d6a6ca74e565672fabf7ad89541071d008b%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/rc998b18880df98bafaade071346690c2bc1444adaa1a1ea464b93f0a%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/rcc44594d4d6579b90deccd4536b5d31f099ef563df39b094be286b9e%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/rd18c3c43602e66f9cdcf09f1de233804975b9572b0456cc582390b6f%40%3Ccvs.httpd.apache.org%3E
- lists.apache.org/thread.html/re1e3a24664d35bcd0a0e793e0b5fc6ca6c107f99a1b2c545c5d4b467%40%3Ccvs.httpd.apache.org%3E
Vendor advisories and official records. Exploit/PoC links are deliberately left out.