CVE-2020-9273
📋 TL;DR
CVE-2020-9273 is a use-after-free vulnerability in ProFTPD 1.3.7 that allows remote attackers to corrupt memory pools by interrupting data transfer channels. This can lead to remote code execution on affected FTP servers. Any organization running vulnerable ProFTPD versions is affected.
💻 Affected Systems
- ProFTPD
📦 What is this software?
Backports Sle by Opensuse
Backports Sle by Opensuse
Fedora by Fedoraproject
Fedora by Fedoraproject
Leap by Opensuse
Proftpd by Proftpd
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker gains full control of the FTP server, potentially leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Server crashes (denial of service) or limited remote code execution with FTP service account privileges.
If Mitigated
If properly segmented and monitored, impact is limited to FTP service disruption with no lateral movement.
🎯 Exploit Status
Exploitation requires interrupting data transfers, which can be done remotely without authentication. Public exploit code exists in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: ProFTPD 1.3.7a or later
Vendor Advisory: http://www.proftpd.org/docs/RELEASE_NOTES-1.3.7a
Restart Required: Yes
Instructions:
1. Download ProFTPD 1.3.7a or later from proftpd.org. 2. Stop ProFTPD service. 3. Install new version following distribution package manager or source compilation. 4. Restart ProFTPD service.
🔧 Temporary Workarounds
Disable FTP service
linuxTemporarily disable ProFTPD until patching can be completed
sudo systemctl stop proftpd
sudo systemctl disable proftpd
Network segmentation
linuxRestrict FTP access to trusted networks only using firewall rules
sudo iptables -A INPUT -p tcp --dport 21 -s TRUSTED_NETWORK -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 21 -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit FTP service exposure
- Monitor for exploitation attempts and implement intrusion detection rules
🔍 How to Verify
Check if Vulnerable:
Check ProFTPD version: proftpd -v or check package manager. If version is exactly 1.3.7, system is vulnerable.Check Version:
proftpd -v 2>&1 | head -1Verify Fix Applied:
Verify ProFTPD version is 1.3.7a or later and service is running without crashes.📡 Detection & Monitoring
Log Indicators:
- Unexpected ProFTPD crashes
- Memory allocation errors in syslog
- Abnormal data transfer interruptions
Network Indicators:
- Multiple FTP connection attempts with interrupted transfers
- Unusual FTP traffic patterns
SIEM Query:
source="proftpd.log" AND ("crash" OR "segmentation fault" OR "use-after-free")🔗 References
- http://lists.opensuse.org/opensuse-security-announce/2020-03/msg00002.html
- http://www.openwall.com/lists/oss-security/2021/08/25/1
- http://www.openwall.com/lists/oss-security/2021/09/06/2
- https://cert-portal.siemens.com/productcert/pdf/ssa-679335.pdf
- https://github.com/proftpd/proftpd/blob/master/RELEASE_NOTES
- https://github.com/proftpd/proftpd/issues/903
- https://lists.debian.org/debian-lts-announce/2020/02/msg00022.html
- https://lists.debian.org/debian-lts-announce/2020/03/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VCUPRYSJR7XOM3HQ6H5M4OGDU7OHCHBF/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XHO3S5WPRRP7VGKIAHLYQVEYW5HRYIJN/
- https://security.gentoo.org/glsa/202003-35
- https://www.debian.org/security/2020/dsa-4635
- http://lists.opensuse.org/opensuse-security-announce/2020-03/msg00002.html
- http://www.openwall.com/lists/oss-security/2021/08/25/1
- http://www.openwall.com/lists/oss-security/2021/09/06/2
- https://cert-portal.siemens.com/productcert/pdf/ssa-679335.pdf
- https://github.com/proftpd/proftpd/blob/master/RELEASE_NOTES
- https://github.com/proftpd/proftpd/issues/903
- https://lists.debian.org/debian-lts-announce/2020/02/msg00022.html
- https://lists.debian.org/debian-lts-announce/2020/03/msg00002.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VCUPRYSJR7XOM3HQ6H5M4OGDU7OHCHBF/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XHO3S5WPRRP7VGKIAHLYQVEYW5HRYIJN/
- https://security.gentoo.org/glsa/202003-35
- https://www.debian.org/security/2020/dsa-4635
