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CVE-2016-4538

33
FAUCET Score

CVE-2016-4538 is a critical vulnerability affecting PHP versions before 5.5.35, 5.6.21, and 7.0.6, specifically within the bcpowmod function of the bcmath extension. This flaw allows remote attackers to trigger a denial of service or potentially other impacts by manipulating global variables through crafted calls. With a CVSS score of 9.8 (CRITICAL), it presents a high risk due to its network-based attack vector, low complexity, and potential for complete compromise of confidentiality, integrity, and availability. While there is no evidence of active exploitation, nor publicly available exploit code in Metasploit, Nuclei, or ExploitDB, the vulnerability has garnered significant community discussion with 10 mentions, indicating awareness among security researchers.

Impacted Technologies

VendorProductVersion(s)CPE
<= 5.5.33CPE matchmatch criteria
cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
5.6.0CPE matchmatch criteria
cpe:2.3:a:php:php:5.6.0:*:*:*:*:*:*:*
5.6.1CPE matchmatch criteria
cpe:2.3:a:php:php:5.6.1:*:*:*:*:*:*:*
5.6.2CPE matchmatch criteria
cpe:2.3:a:php:php:5.6.2:*:*:*:*:*:*:*
5.6.3CPE matchmatch criteria
cpe:2.3:a:php:php:5.6.3:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.0

9.8CRITICAL

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.0

Exploit Intelligence

EPSS Score
6.23%
Probability of exploitation in next 30 days
EPSS Percentile
92.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-25
Model: v2026.06.15
This CVE's current EPSS score of 0.0623 is in the 87th percentile among its peer group of 36,833 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (21)

redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6Fixed in: rh-php56-0:2.3-1.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6Fixed in: rh-php56-php-0:5.6.25-1.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6Fixed in: rh-php56-php-pear-1:1.9.5-4.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUSFixed in: rh-php56-0:2.3-1.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUSFixed in: rh-php56-php-0:5.6.25-1.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 6.7 EUSFixed in: rh-php56-php-pear-1:1.9.5-4.el6
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-php56-0:2.3-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-php56-php-0:5.6.25-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7Fixed in: rh-php56-php-pear-1:1.9.5-4.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUSFixed in: rh-php56-0:2.3-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUSFixed in: rh-php56-php-0:5.6.25-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.2 EUSFixed in: rh-php56-php-pear-1:1.9.5-4.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.3 EUSFixed in: rh-php56-0:2.3-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.3 EUSFixed in: rh-php56-php-0:5.6.25-1.el7
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Software Collections for Red Hat Enterprise Linux 7.3 EUSFixed in: rh-php56-php-pear-1:1.9.5-4.el7
View patch
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: php
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: php53
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 6Fixed in: php
redhatend of lifevia redhat_api
Product: Red Hat Enterprise Linux 7Fixed in: php
redhatend of lifevia redhat_api
Product: Red Hat Software CollectionsFixed in: php54-php
redhatend of lifevia redhat_api
Product: Red Hat Software CollectionsFixed in: php55-php

Vendor Advisories (1)

redhatCVE-2016-4538Low

php: bcpowmod accepts negative scale causing heap buffer overflow corrupting _one_ definition

Apr 24, 2016

References

lists.fedoraproject.org / pipermail/package-announce/2016-May/183736.html
lists.opensuse.org / opensuse-updates/2016-05/msg00086.html
lists.opensuse.org / opensuse-updates/2016-06/msg00027.html
php.net / ChangeLog-5.php
Patch
php.net / ChangeLog-7.php
Patch
rhn.redhat.com / errata/RHSA-2016-2750.html
bugs.php.net / bug.php
Exploit
git.php.net
h20566.www2.hpe.com / portal/site/hpsc/public/kb/docDisplay
h20566.www2.hpe.com / portal/site/hpsc/public/kb/docDisplay
h20566.www2.hpe.com / portal/site/hpsc/public/kb/docDisplay
security.gentoo.org / glsa/201611-22
debian.org / security/2016/dsa-3602
openwall.com / lists/oss-security/2016/05/05/21
securityfocus.com / bid/90173