How severe is CVE-2016-4538?

CVE-2016-4538 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2016-4538 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 6% (93rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-4538?

CVE-2016-4538 primarily affects Php. In total, 30 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2016-4538?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2016-4538 published?

CVE-2016-4538 was published on 2016-05-22 and last updated on 2026-06-17.

CVE-2016-4538

CVE-2016-4538 is a critical-severity vulnerability in Php with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 6% (93rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Php
Published: 2016-05-22
Last modified: 2026-06-17

Description

The bcpowmod function in ext/bcmath/bcmath.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 modifies certain data structures without considering whether they are copies of the _zero_, _one_, or _two_ global variable, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted call.

Frequently asked questions

What is CVE-2016-4538?: The bcpowmod function in ext/bcmath/bcmath.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 modifies certain data structures without considering whether they are copies of the _zero_, _one_, or _two_ global variable, which allows remote attackers to cause a denial of service or possibly have unspecified other impact via a crafted call.
How severe is CVE-2016-4538?: CVE-2016-4538 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2016-4538 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 6% (93rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-4538?: CVE-2016-4538 primarily affects Php. In total, 30 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2016-4538?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2016-4538 published?: CVE-2016-4538 was published on 2016-05-22 and last updated on 2026-06-17.

References

Affected products (30)

cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.1:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.2:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.3:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.4:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.5:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.6:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.7:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.8:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.9:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.10:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.11:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.12:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.13:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.14:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.15:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.16:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.17:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.18:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.19:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.20:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.0:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.1:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.2:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.3:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.4:*:*:*:*:*:*:*
cpe:2.3:a:php:php:7.0.5:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:24:*:*:*:*:*:*:*
cpe:2.3:o:opensuse:leap:42.1:*:*:*:*:*:*:*

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Threat intelligence

Threat-intel indicators referencing this CVE:

45.84.120.3 (ipv4-addr)
79.137.34.248 (ipv4-addr)
221.161.235.168 (ipv4-addr)
200.196.50.91 (ipv4-addr)
187.51.208.158 (ipv4-addr)
187.141.71.166 (ipv4-addr)
187.110.238.50 (ipv4-addr)
113.164.66.10 (ipv4-addr)