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Fencer Intel
critical 9.8

CVE-2016-4538 in the critical feed json

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 structur…

published 2016-05-22 10 y ago modified 2026-06-17 4 mo ago also EUVD-2016-5525

cvss
9.8
version 3.0, NVD
cisa kev
Not listed
not in CISA's catalog
epss
6.1%
EPSS 6.1% chance of exploitation in 30 days, percentile 93%
public exploits
0
none known

Summary

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.

Patch / fix

  • php5 Ubuntu 14.04 LTS 5.5.9+dfsg-1ubuntu4.17
  • php7.0 Ubuntu 16.04 LTS 7.0.4-7ubuntu2.1

ubuntu advisories UBUNTU-CVE-2016-4538

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • rh-php56 RHEL 2 SOFTWARE_COLLECTIONS 2.3-1.el6
  • rh-php56 RHEL 2 SOFTWARE_COLLECTIONS 2.3-1.el7
  • rh-php56-php RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el6
  • rh-php56-php RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el7
  • rh-php56-php-gd RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el6
  • rh-php56-php-gd RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el7
  • rh-php56-php-cli RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el6
  • rh-php56-php-cli RHEL 2 SOFTWARE_COLLECTIONS 5.6.25-1.el7

red hat advisories RHSA-2016:2750

  • php53 SLES for SAP 11 SP4, SLES 11 SP4, SLES 11 SP3-TERADATA +5 more 5.3.17-71.1
  • php5 SLE Software Development Kit 12 SP1, SLE Software Development Kit 12, SLE Module for Web and Scripting 12 5.5.14-59.2
  • php53 SLES 11 SP2-LTSS 5.3.17-47.1

suse advisories SUSE-SU-2016:1638-1SUSE-SU-2016:1581-1SUSE-SU-2016:1504-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2016-4538 updated cvss 2.6

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

  • Red Hat Enterprise Linux 5 php, php53 Red Hat Enterprise Linux 6 php, php-gd, php-cli, php-dba, php-fpm, php-pdo, +20 more Red Hat Enterprise Linux 7 php, php-gd, php-cli, php-dba, php-fpm, php-pdo, +18 more Red Hat Software Collections php54-php, php55-php, php54-php-gd, php55-php-gd, php54-php-cli, php54-php-dba, +44 more
    affected: no fix planned “Will not fix”
  • Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 6) rh-php56 2.3-1.el6, rh-php56-php 5.6.25-1.el6, rh-php56-runtime 2.3-1.el6, rh-php56-scldevel 2.3-1.el6, rh-php56-php-gd 5.6.25-1.el6, rh-php56-php-cli 5.6.25-1.el6, +26 more Red Hat Software Collections for Red Hat Enterprise Linux Server (v. 7) rh-php56 2.3-1.el7, rh-php56-php 5.6.25-1.el7, rh-php56-runtime 2.3-1.el7, rh-php56-scldevel 2.3-1.el7, rh-php56-php-gd 5.6.25-1.el7, rh-php56-php-cli 5.6.25-1.el7, +24 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 6.7) rh-php56 2.3-1.el6, rh-php56-php 5.6.25-1.el6, rh-php56-runtime 2.3-1.el6, rh-php56-scldevel 2.3-1.el6, rh-php56-php-gd 5.6.25-1.el6, rh-php56-php-cli 5.6.25-1.el6, +26 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.2) rh-php56 2.3-1.el7, rh-php56-php 5.6.25-1.el7, rh-php56-runtime 2.3-1.el7, rh-php56-scldevel 2.3-1.el7, rh-php56-php-gd 5.6.25-1.el7, rh-php56-php-cli 5.6.25-1.el7, +24 more Red Hat Software Collections for Red Hat Enterprise Linux Server EUS (v. 7.3) rh-php56 2.3-1.el7, rh-php56-php 5.6.25-1.el7, rh-php56-runtime 2.3-1.el7, rh-php56-scldevel 2.3-1.el7, rh-php56-php-gd 5.6.25-1.el7, rh-php56-php-cli 5.6.25-1.el7, +24 more Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 6) rh-php56 2.3-1.el6, rh-php56-php 5.6.25-1.el6, rh-php56-runtime 2.3-1.el6, rh-php56-scldevel 2.3-1.el6, rh-php56-php-gd 5.6.25-1.el6, rh-php56-php-cli 5.6.25-1.el6, +26 more
    +1 more products
    Red Hat Software Collections for Red Hat Enterprise Linux Workstation (v. 7) rh-php56 2.3-1.el7, rh-php56-php 5.6.25-1.el7, rh-php56-runtime 2.3-1.el7, rh-php56-scldevel 2.3-1.el7, rh-php56-php-gd 5.6.25-1.el7, rh-php56-php-cli 5.6.25-1.el7, +24 more
    fixed: vendor fix RHSA-2016:2750

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

6.06% chance of exploitation in the next 30 days, higher than 93% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • bugs.php.net https://bugs.php.net/bug.php?id=72093 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.0 9.8 CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-20 Improper Input Validation
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.