CVE-2016-4538

Severity: critical (CVSS 9.8 v3.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 6.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2016-05-22 · updated 2026-06-17
Weakness: CWE-20

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.

Affected products

Fedoraproject Fedora: 24
openSUSE Leap: 42.1
PHP: through 5.5.33; 5.6.0, 5.6.1, 5.6.2, 5.6.3, 5.6.4, 5.6.5 (+21)

References

http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183736.html
http://lists.opensuse.org/opensuse-updates/2016-05/msg00086.html
http://lists.opensuse.org/opensuse-updates/2016-06/msg00027.html
http://php.net/ChangeLog-5.php
http://php.net/ChangeLog-7.php
http://rhn.redhat.com/errata/RHSA-2016-2750.html
http://www.debian.org/security/2016/dsa-3602
http://www.openwall.com/lists/oss-security/2016/05/05/21
http://www.securityfocus.com/bid/90173
https://bugs.php.net/bug.php?id=72093
https://git.php.net/?p=php-src.git%3Ba=commit%3Bh=d650063a0457aec56364e4005a636dc6c401f9cd
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05240731

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