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.
The MITRE CVE dictionary describes this issue as:
Find out more about CVE-2017-8923 from the MITRE CVE dictionary dictionary and NIST NVD.
NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.
| CVSS3 Base Score | 7.5 |
|---|---|
| CVSS3 Base Metrics | CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| Attack Vector | Network |
| Attack Complexity | Low |
| Privileges Required | None |
| User Interaction | None |
| Scope | Unchanged |
| Confidentiality | None |
| Integrity Impact | None |
| Availability Impact | High |
| Platform | Package | State |
|---|---|---|
| Red Hat Software Collections for Red Hat Enterprise Linux | rh-php70-php | Will not fix |
| Red Hat Software Collections for Red Hat Enterprise Linux | rh-php56-php | Not affected |
| Red Hat OpenShift Enterprise 2 | php | Not affected |
| Red Hat Enterprise Linux 7 | php | Not affected |
| Red Hat Enterprise Linux 6 | php | Not affected |
| Red Hat Enterprise Linux 5 | php53 | Not affected |
| Red Hat Enterprise Linux 5 | php | Not affected |
Vulmon