CVE-2019-9023
📋 TL;DR
This CVE describes heap-based buffer over-read vulnerabilities in PHP's mbstring regular expression functions when processing invalid multibyte data. Attackers could exploit these vulnerabilities to cause denial of service or potentially execute arbitrary code. Affected systems include PHP versions before 5.6.40, 7.x before 7.1.26, 7.2.x before 7.2.14, and 7.3.x before 7.3.1.
💻 Affected Systems
- PHP
📦 What is this software?
Leap by Opensuse
Php by Php
Php by Php
Php by Php
Php by Php
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
Ubuntu Linux by Canonical
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, or persistent backdoor installation.
Likely Case
Denial of service (application crash) or information disclosure through memory leaks.
If Mitigated
Limited impact with proper input validation and WAF filtering, potentially only causing application instability.
🎯 Exploit Status
Exploitation requires crafting specific invalid multibyte regular expression patterns. Public exploit details exist in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: PHP 5.6.40, 7.1.26, 7.2.14, 7.3.1
Vendor Advisory: https://www.php.net/ChangeLog-7.php#7.3.1
Restart Required: Yes
Instructions:
1. Identify current PHP version. 2. Upgrade to patched version using package manager (apt-get upgrade php, yum update php). 3. Restart web server (apache2 restart, systemctl restart nginx). 4. Verify upgrade with php -v.
🔧 Temporary Workarounds
Disable mbstring extension
allTemporarily disable vulnerable mbstring functions if not required
php -i | grep mbstring
Edit php.ini: extension=mbstring.so to ;extension=mbstring.so
Restart web server
Input validation filter
allImplement strict input validation for multibyte regular expression patterns
Implement PHP filter_var() with FILTER_SANITIZE_STRING before mbstring processing
🧯 If You Can't Patch
- Implement Web Application Firewall (WAF) rules to block suspicious multibyte pattern inputs
- Isolate vulnerable PHP applications in restricted network segments with minimal privileges
🔍 How to Verify
Check if Vulnerable:
Run php -v and compare version against affected ranges. Check if mbstring extension is enabled with php -m | grep mbstring.Check Version:
php -v | head -1Verify Fix Applied:
Confirm PHP version is 5.6.40+, 7.1.26+, 7.2.14+, or 7.3.1+ using php -v command.📡 Detection & Monitoring
Log Indicators:
- Segmentation fault errors in PHP/webserver logs
- Unusual memory access patterns
- Multiple failed mbstring function calls
Network Indicators:
- HTTP requests containing crafted multibyte patterns in parameters
- Unusual traffic spikes to PHP endpoints
SIEM Query:
source="php_error.log" AND ("segmentation fault" OR "buffer over-read" OR "mbstring")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00083.html
- http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00104.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00041.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00044.html
- http://www.securityfocus.com/bid/107156
- https://access.redhat.com/errata/RHSA-2019:2519
- https://access.redhat.com/errata/RHSA-2019:3299
- https://bugs.php.net/bug.php?id=77370
- https://bugs.php.net/bug.php?id=77371
- https://bugs.php.net/bug.php?id=77381
- https://bugs.php.net/bug.php?id=77382
- https://bugs.php.net/bug.php?id=77385
- https://bugs.php.net/bug.php?id=77394
- https://bugs.php.net/bug.php?id=77418
- https://security.netapp.com/advisory/ntap-20190321-0001/
- https://support.f5.com/csp/article/K06372014
- https://usn.ubuntu.com/3902-1/
- https://usn.ubuntu.com/3902-2/
- https://www.debian.org/security/2019/dsa-4398
- http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00083.html
- http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00104.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00041.html
- http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00044.html
- http://www.securityfocus.com/bid/107156
- https://access.redhat.com/errata/RHSA-2019:2519
- https://access.redhat.com/errata/RHSA-2019:3299
- https://bugs.php.net/bug.php?id=77370
- https://bugs.php.net/bug.php?id=77371
- https://bugs.php.net/bug.php?id=77381
- https://bugs.php.net/bug.php?id=77382
- https://bugs.php.net/bug.php?id=77385
- https://bugs.php.net/bug.php?id=77394
- https://bugs.php.net/bug.php?id=77418
- https://security.netapp.com/advisory/ntap-20190321-0001/
- https://support.f5.com/csp/article/K06372014
- https://usn.ubuntu.com/3902-1/
- https://usn.ubuntu.com/3902-2/
- https://www.debian.org/security/2019/dsa-4398
