CVE-2020-12823
📋 TL;DR
CVE-2020-12823 is a buffer overflow vulnerability in OpenConnect VPN client versions 8.09 and earlier. Attackers can exploit this by sending crafted certificate data to cause denial of service (application crash) or potentially execute arbitrary code. Users running vulnerable OpenConnect versions are affected.
💻 Affected Systems
- OpenConnect VPN client
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Fedora by Fedoraproject
Leap by Opensuse
Leap by Opensuse
Openconnect by Infradead
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise if the buffer overflow can be controlled to execute arbitrary code.
Likely Case
Denial of service through application crash, disrupting VPN connectivity.
If Mitigated
Limited to application crash if exploit controls only trigger buffer overflow without code execution.
🎯 Exploit Status
Exploitation requires crafting malicious certificate data, but no public exploit code is documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.10 and later
Vendor Advisory: https://gitlab.com/openconnect/openconnect/-/merge_requests/108
Restart Required: Yes
Instructions:
1. Update OpenConnect to version 8.10 or later using your package manager. 2. For Debian/Ubuntu: sudo apt update && sudo apt upgrade openconnect. 3. For RHEL/CentOS: sudo yum update openconnect. 4. Restart any OpenConnect VPN connections.
🔧 Temporary Workarounds
Disable vulnerable certificate parsing
allAvoid connecting to untrusted VPN servers that could provide malicious certificates.
🧯 If You Can't Patch
- Restrict OpenConnect usage to trusted VPN servers only.
- Monitor for OpenConnect crashes and investigate any anomalies.
🔍 How to Verify
Check if Vulnerable:
Check OpenConnect version with: openconnect --version | head -1Check Version:
openconnect --version | head -1Verify Fix Applied:
Verify version is 8.10 or higher with: openconnect --version📡 Detection & Monitoring
Log Indicators:
- OpenConnect process crashes
- Segmentation fault errors in system logs
- Unexpected VPN disconnections
Network Indicators:
- Unusual certificate data sent to OpenConnect client
- Traffic from untrusted VPN servers
SIEM Query:
process.name:"openconnect" AND (event.action:"crashed" OR log.level:"error")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00039.html
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00056.html
- https://bugs.gentoo.org/721570
- https://gitlab.com/openconnect/openconnect/-/merge_requests/108
- https://lists.debian.org/debian-lts-announce/2020/05/msg00015.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/25MFX4AZE7RDCUWOL4ZOE73YBOPUMQDX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AYSXLXAPXD2T73T6JMHI5G2WP7KHAGMN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BEVTIH5UFX35CC7MVSYBGRM3D66ACFD5/
- https://security.gentoo.org/glsa/202006-15
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00039.html
- http://lists.opensuse.org/opensuse-security-announce/2020-07/msg00056.html
- https://bugs.gentoo.org/721570
- https://gitlab.com/openconnect/openconnect/-/merge_requests/108
- https://lists.debian.org/debian-lts-announce/2020/05/msg00015.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/25MFX4AZE7RDCUWOL4ZOE73YBOPUMQDX/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/AYSXLXAPXD2T73T6JMHI5G2WP7KHAGMN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BEVTIH5UFX35CC7MVSYBGRM3D66ACFD5/
- https://security.gentoo.org/glsa/202006-15
