CVE-2015-4021
MEDIUMEPSS 97th pctlDescription
The phar_parse_tarfile function in ext/phar/tar.c in PHP before 5.4.41, 5.5.x before 5.5.25, and 5.6.x before 5.6.9 does not verify that the first character of a filename is different from the \0 character, which allows remote attackers to cause a denial of service (integer underflow and memory corruption) via a crafted entry in a tar archive.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v2 Vector
No CVSS vector data available.
Exploit Intelligence
Very high risk: more likely to be exploited than 97% of all known CVEs.
References
Related Vulnerabilities
Other CWE-189 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2015-1538 | High | 10.0 | 99% | - | - |
| CVE-2006-3747 | High | 7.6 | 96% | - | Fix |
| CVE-2007-0071 | High | 9.3 | 93% | - | - |
| CVE-2015-3829 | High | 10.0 | 90% | - | - |
| CVE-2015-3864 | High | 10.0 | 87% | - | - |
| CVE-2015-1539 | High | 10.0 | 86% | - | - |
Common questions
How do I fix CVE-2015-4021?
Published advisories record a fix for 5 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2015-4021 being actively exploited?
Not that we know of. CVE-2015-4021 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 21.4% is the estimated probability that it will be exploited in the next 30 days. That is higher than 97% of all scored CVEs.
How severe is CVE-2015-4021?
CVE-2015-4021 has a CVSS v2 base score of 5.0, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2015-4021 affect?
Published advisories record a fix for libapache2-mod-php5 (Ubuntu), php5 (Ubuntu), php5-cgi (Ubuntu), php5-cli (Ubuntu), and 1 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-06.