CVE-2015-4024

Public exploit available. Not confirmed exploited in the wild yet. A vendor fix is available.

CVSS 2.05.0Medium EPSS percentile99th50% chance in 30 days CISA KEVNot listedNo confirmed exploitation
Public exploit: 1 source FixVendor fixNo build named by the sources

Published 2015-06-09Updated 2026-05-06Sources: CVE.org, NVD, BDU

NVD CVE.org

What to do

The vendor has published a fix. Version details are below where the sources state them.

Apple Mac Os XAffected: ≤ 10.10.4Upgrade to: after 10.10.4Stated by: NVD
PhpAffected: ≤ 5.4.40Upgrade to: after 5.4.40Stated by: NVD
Hp System Management HomepageAffected: ≤ 7.5.3.1Upgrade to: after 7.5.3.1Stated by: NVD
Canonical Ltd. UbuntuAffected: 14.10Upgrade to: not statedStated by: BDU
Red Hat Inc. Red Hat Enterprise LinuxAffected: 6Upgrade to: not statedStated by: BDU

Versions as the sources state them. 1 more product has version data. Full version matrix after sign-in

Steps

Written by AI from the record

Check the PHP version used by every web server that accepts file uploads or web forms.
Upgrade PHP 5.4 to 5.4.41, PHP 5.5 to 5.5.25, or PHP 5.6 to 5.6.9 or later; preferably move to a currently supported PHP release.
If an immediate upgrade is not possible, restrict large or repeated form submissions at the web server or firewall and limit upload request sizes.
Review server CPU and web-request logs for unusual bursts of large form submissions after mitigation.

Vendor advisory Some work to apply

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

Algorithmic complexity vulnerability in the multipart_buffer_headers function in main/rfc1867.c in PHP before 5.4.41, 5.5.x before 5.5.25, and 5.6.x before 5.6.9 allows remote attackers to cause a denial of service (CPU consumption) via crafted form data that triggers an improper order-of-growth outcome.

In plain language

Written by AI from the record

This is a PHP flaw that can let someone overload a website with specially made form submissions if it runs PHP before 5.4.41, 5.5.25, or 5.6.9; a typical business should act if it still uses these retired versions.

Algorithmic-complexity denial of service in PHP's multipart_buffer_headers handling allows remote CPU exhaustion through crafted multipart form data.

If you're affected

Website becomes unresponsive
Online forms stop working
High server CPU costs
Customer service disruption

What is it

PHP can be tricked into spending too much time examining a specially constructed web form submission. It is like a customer handing a receptionist a form designed to make them repeatedly reread every line, leaving them unable to help anyone else.

Who is affected

This matters to you if your website or application runs PHP and accepts web forms, especially forms that allow file uploads. It is only a risk if an attacker can reach those forms over the internet.

How urgent is it

A public exploit is available, so treat this as an amber-priority issue and schedule remediation promptly. It is not listed in CISA's catalog of vulnerabilities known to be actively exploited, but vulnerable retired PHP installations remain an attractive target for service disruption.

What to do — in detail

Confirm the PHP runtime version on each web server and identify internet-facing endpoints that process multipart/form-data, particularly upload and contact forms. Upgrade the applicable legacy branch to PHP 5.4.41, PHP 5.5.25, or PHP 5.6.9 at minimum; because all of these branches are end-of-life, plan a tested migration to a supported PHP release rather than stopping at the minimum fix. Test the application in staging before a major-version migration, as application compatibility changes may be required. If patching is delayed, apply web-server or WAF limits for request body size, upload size, request rate, and concurrent uploads; restrict exposed upload endpoints where practical. No CISA KEV remediation due date applies. Monitor web-server access logs and host CPU usage for repeated or unusually large multipart POST requests.

Technical context

CVE-2015-4024 is a CVSS 5.0 medium-severity, network-reachable denial-of-service issue (CWE-399) in PHP's multipart_buffer_headers function in main/rfc1867.c. Crafted multipart form data triggers unfavorable algorithmic growth and CPU consumption. A public exploit is known to be available. CISA KEV does not list this CVE. EPSS predicts a 49.9% likelihood and places it in the 99th percentile, with a falling trend.

This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.