CVE-2016-4538

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.

Exploit odds

6.1% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2016-05-22 01:59 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 00:47 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 6.1% in the next 30 days (EPSS).
• Severity: 9.8 CRITICAL (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2016-05-22 01:59 UTC

Last modified

2026-06-17 00:47 UTC

Exploit probability

6.1% · EPSS, next 30 days

Weakness

CWE-20 · Improper input validation

Record status

Modified

Affected

• PHP ≤ 5.5.33
• PHP 5.6.0
• PHP 5.6.1
• PHP 5.6.2
• PHP 5.6.3
• PHP 5.6.4
• PHP 5.6.5
• PHP 5.6.6

Attack profile CVSS 3.0 · 9.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2016-4538.md and follow it. Check whether this project is affected by CVE-2016-4538. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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