CVE-2016-4979

CVE-2016-4979 is a high-severity vulnerability in Apache Http Server with a CVSS 3.x base score of 7.5. Its EPSS exploit-prediction score of 19% places it in the 97th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-284.

Key facts

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.

Frequently asked questions

What is 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 restrictions by leveraging the ability to send multiple requests over a single connection and aborting a renegotiation.
How severe is CVE-2016-4979?
CVE-2016-4979 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability none.
Is CVE-2016-4979 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 19% (97th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4979?
CVE-2016-4979 primarily affects Apache Http Server. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4979?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2016-4979 published?
CVE-2016-4979 was published on 2016-07-06 and last updated on 2026-06-17.

References

Affected products (3)

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Threat intelligence

Threat-intel indicators referencing this CVE: