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Vulnerabilities

Vulnerability · 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 re…

Published Jul 6, 2016 · catalog updated Jun 17, 2026 · http server

Last checked Nov 8, 2026. A connected source was read within the last 7 days.

Check this week

CVE-2016-4979 is not in CISA KEV. FIRST estimates a 18.80% chance of exploitation in the next 30 days. Check whether you run http server.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
18.80%
Remediation
Advisory link
Affected products
cpe 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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe apache/http server2.4.18
  • cpe apache/http server2.4.19
  • cpe apache/http server2.4.20

How to fix CVE-2016-4979

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

CVE-2016-4979 is not in CISA KEV. FIRST estimates a 18.80% chance of exploitation in the next 30 days. Check whether you run http server.

Which versions are affected?

Compare what you have installed with apache/http server 2.4.18; apache/http server 2.4.19; apache/http server 2.4.20. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-284: Improper Access Control. EPSS 18.80%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Apache HTTP Server security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Jul 6, 2016 · Monitored products — critical

    Detected

    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.

  2. Jun 17, 2026 · Monitored products — critical

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2016-4979

    Official CVE identifier

    cve.org
  • Monitored products — criticalVendor advisoryCVE-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 restrictions by leveraging the ability to send multiple requests over a single connection and aborting a renegotiation.

    nvd.nist.gov
  • Packet Storm SecurityCited referencehttp://packetstormsecurity.com/files/137771/Apache-2.4.20-X509-Authentication-Bypass.html

    Packet Storm link already published on the finding.

    packetstormsecurity.com

References

Freshness

Last verified in this catalog Nov 7, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • Packet Storm SecurityNov 8, 2026
  • CVE.orgNov 4, 2026
  • Monitored products — criticalNov 4, 2026