CVE-2021-36777
📋 TL;DR
This vulnerability in openSUSE Build Service login proxy allows attackers to create fake login forms that capture user credentials in plain text and send them to attacker-controlled servers. It affects users of openSUSE Build Service versions prior to the fixed commit. Attackers can steal credentials from legitimate users attempting to authenticate.
💻 Affected Systems
- openSUSE Build Service login-proxy-scripts
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers steal administrative credentials, gain full control of the build service infrastructure, and potentially compromise downstream software packages.
Likely Case
Attackers capture user credentials, gain unauthorized access to build service accounts, and potentially inject malicious code into software packages.
If Mitigated
With proper network segmentation and monitoring, credential theft is detected before attackers can use stolen credentials for further access.
🎯 Exploit Status
Exploitation requires tricking users into interacting with a malicious login form, making it a social engineering component.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Commit dc000cdfe9b9b715fb92195b1a57559362f689ef or later
Vendor Advisory: https://bugzilla.suse.com/show_bug.cgi?id=1191209
Restart Required: Yes
Instructions:
1. Update openSUSE Build Service to version containing commit dc000cdfe9b9b715fb92195b1a57559362f689ef or later. 2. Restart the login proxy service. 3. Verify the fix by checking the commit hash in the installed version.
🔧 Temporary Workarounds
Disable Login Proxy
linuxTemporarily disable the vulnerable login proxy component if not essential.
systemctl stop login-proxy
systemctl disable login-proxy
Network Access Control
linuxRestrict network access to the login proxy to trusted IP ranges only.
iptables -A INPUT -p tcp --dport [login-proxy-port] -s [trusted-ip-range] -j ACCEPT
iptables -A INPUT -p tcp --dport [login-proxy-port] -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate the build service from untrusted networks.
- Deploy web application firewalls (WAF) to detect and block credential harvesting attempts.
🔍 How to Verify
Check if Vulnerable:
Check the git commit hash of the installed login-proxy-scripts package; if earlier than dc000cdfe9b9b715fb92195b1a57559362f689ef, it is vulnerable.Check Version:
git log --oneline -1 /path/to/login-proxy-scriptsVerify Fix Applied:
Verify the commit hash is dc000cdfe9b9b715fb92195b1a57559362f689ef or later after patching.📡 Detection & Monitoring
Log Indicators:
- Unusual login attempts from unexpected IP addresses
- Log entries showing credential submissions to non-standard endpoints
Network Indicators:
- Outbound HTTP/HTTPS connections from the login proxy to unknown external servers
- Suspicious redirect patterns in login flows
SIEM Query:
source="login-proxy" AND (url="*malicious-domain*" OR dest_ip="[external-ip-range]")