Ref: https://nvd.nist.gov/vuln/detail/CVE-2017-8923
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Description

The zend_string_extend function in Zend/zend_string.h in PHP through 7.1.5 does
not prevent changes to string objects that result in a negative length, which
allows remote attackers to cause a denial of service (application crash) or
possibly have unspecified other impact by leveraging a script's use of .= with
a long string.
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Hyperlink

[1] https://bugs.php.net/bug.php?id=74577

[2] https://bugs.php.net/bug.php?id=73122

[3] https://security-tracker.debian.org/tracker/CVE-2017-8923

Bug ID	1038980
Summary	VUL-0: CVE-2017-8923: php7: denial of service (application crash) by using .= with a long string (zend_string_extend func in Zend/zend_string.h)
Classification	openSUSE
Product	openSUSE Distribution
Version	Leap 42.2
Hardware	Other
OS	Other
Status	NEW
Severity	Normal
Priority	P5 - None
Component	Security
Assignee	security-team@suse.de
Reporter	mikhail.kasimov@gmail.com
QA Contact	qa-bugs@suse.de
Found By	---
Blocker	---