What is CVE-2016-4539?

CVE-2016-4539 is a critical-severity vulnerability in PHP, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2016-05-22.

How severe is CVE-2016-4539?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2016-4539 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Buffer overflow in PHP

CVE-2016-4539

The xml_parse_into_struct function in ext/xml/xml.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 allows remote attackers to cause a denial of service (buffer under-read and segmentation fault) or possibly have unspecified other impact via crafted XML data in the second argument, leading to a parser level of zero.

Vulnerability class: Buffer Overflow

Published 2016-05-22 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.062 (93.3th percentile), scored 2026-09-29.

Low probability of exploitation in the next 30 days, but still tracked. 93rd percentile — 93.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.062 · newest: 0.062 · change: 0.000

Affected products

PHP — versions 5.6.0, 5.6.1, 5.6.2
Fedoraproject Fedora — versions 24
openSUSE Leap — versions 42.1

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

Public proof-of-concept exploits

References

h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay
lists.opensuse.org/opensuse-updates/2016-06/msg00027.html (vendor-advisory)
security.gentoo.org/glsa/201611-22 (vendor-advisory)
rhn.redhat.com/errata/RHSA-2016-2750.html (vendor-advisory)
www.openwall.com/lists/oss-security/2016/05/05/21 (mailing-list)
www.debian.org/security/2016/dsa-3602 (vendor-advisory)
php.net/ChangeLog-5.php (Patch)
h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay
www.securityfocus.com/bid/90174 (vdb-entry)
php.net/ChangeLog-7.php (Patch)

Frequently asked questions

What is CVE-2016-4539?: CVE-2016-4539 is a critical-severity vulnerability in PHP, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2016-05-22.
How severe is CVE-2016-4539?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2016-4539 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.