CVE-2021-3518
📋 TL;DR
A use-after-free vulnerability in libxml2 versions before 2.9.11 allows attackers to submit crafted XML files to applications using this library, potentially leading to arbitrary code execution. This affects any software that processes XML input with vulnerable libxml2 versions. The impact compromises confidentiality, integrity, and availability of affected systems.
💻 Affected Systems
- libxml2
- Applications using libxml2 library
📦 What is this software?
Clustered Data Ontap Antivirus Connector by Netapp
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Communications Cloud Native Core Network Function Cloud Native Environment by Oracle
View all CVEs affecting Communications Cloud Native Core Network Function Cloud Native Environment →
Enterprise Manager Base Platform by Oracle
Enterprise Manager Base Platform by Oracle
Fedora by Fedoraproject
Fedora by Fedoraproject
Libxml2 by Xmlsoft
Manageability Software Development Kit by Netapp
View all CVEs affecting Manageability Software Development Kit →
Ontap Select Deploy Administration Utility by Netapp
View all CVEs affecting Ontap Select Deploy Administration Utility →
Peoplesoft Enterprise Peopletools by Oracle
Snapdrive by Netapp
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data exfiltration, and persistent backdoor installation.
Likely Case
Application crash causing denial of service, with potential for limited code execution depending on application context.
If Mitigated
Application crash without code execution if memory protections are enabled, but still causing availability impact.
🎯 Exploit Status
Exploitation requires submitting crafted XML files to vulnerable applications. Multiple proof-of-concept examples exist in public disclosures.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.9.11 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1954242
Restart Required: Yes
Instructions:
1. Update libxml2 package to version 2.9.11 or later. 2. Restart affected applications. 3. Recompile any statically linked applications with patched library.
🔧 Temporary Workarounds
Disable XML processing
allDisable XML parsing functionality in applications where not required
Input validation
allImplement strict input validation for XML files before processing
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable systems
- Deploy web application firewall with XML parsing protection rules
🔍 How to Verify
Check if Vulnerable:
Check libxml2 version: xml2-config --version or rpm -q libxml2Check Version:
xml2-config --version || rpm -q libxml2 || dpkg -l libxml2Verify Fix Applied:
Verify version is 2.9.11 or later and test XML processing functionality📡 Detection & Monitoring
Log Indicators:
- Application crashes during XML processing
- Memory access violation errors
- Unusual XML file uploads
Network Indicators:
- Large XML file uploads to web applications
- XML parsing errors in HTTP responses
SIEM Query:
source="application_logs" AND ("libxml2" OR "xml_parse") AND ("segmentation fault" OR "use-after-free" OR "memory corruption")🔗 References
- http://seclists.org/fulldisclosure/2021/Jul/54
- http://seclists.org/fulldisclosure/2021/Jul/55
- http://seclists.org/fulldisclosure/2021/Jul/58
- http://seclists.org/fulldisclosure/2021/Jul/59
- https://bugzilla.redhat.com/show_bug.cgi?id=1954242
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2021/05/msg00008.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOMV5J4PMZAORVT64BKLV6YIZAFDGX6/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4UJ3376I6ZVOYMHBNX4GY3NIV52WV/
- https://security.gentoo.org/glsa/202107-05
- https://security.netapp.com/advisory/ntap-20210625-0002/
- https://support.apple.com/kb/HT212601
- https://support.apple.com/kb/HT212602
- https://support.apple.com/kb/HT212604
- https://support.apple.com/kb/HT212605
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://www.oracle.com/security-alerts/cpuoct2021.html
- http://seclists.org/fulldisclosure/2021/Jul/54
- http://seclists.org/fulldisclosure/2021/Jul/55
- http://seclists.org/fulldisclosure/2021/Jul/58
- http://seclists.org/fulldisclosure/2021/Jul/59
- https://bugzilla.redhat.com/show_bug.cgi?id=1954242
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.debian.org/debian-lts-announce/2021/05/msg00008.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOMV5J4PMZAORVT64BKLV6YIZAFDGX6/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4UJ3376I6ZVOYMHBNX4GY3NIV52WV/
- https://security.gentoo.org/glsa/202107-05
- https://security.netapp.com/advisory/ntap-20210625-0002/
- https://support.apple.com/kb/HT212601
- https://support.apple.com/kb/HT212602
- https://support.apple.com/kb/HT212604
- https://support.apple.com/kb/HT212605
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://www.oracle.com/security-alerts/cpuoct2021.html
