CVE-2021-34555
📋 TL;DR
CVE-2021-34555 is a denial-of-service vulnerability in OpenDMARC where remote attackers can crash the application by sending email messages with multi-value From header fields. This affects OpenDMARC installations processing incoming email, potentially disrupting email authentication services. Organizations using vulnerable OpenDMARC versions for DMARC validation are impacted.
💻 Affected Systems
- OpenDMARC
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Opendmarc by Trusteddomain
Opendmarc by Trusteddomain
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage of OpenDMARC processing, causing email authentication failures and potential email delivery disruptions for dependent systems.
Likely Case
Intermittent crashes of OpenDMARC processes when processing malicious emails, leading to temporary service disruptions.
If Mitigated
Minimal impact with proper network controls and updated software, maintaining normal email authentication functionality.
🎯 Exploit Status
Exploitation requires sending specially crafted email messages to trigger the vulnerability. The issue is well-documented in public repositories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.4.2 and later
Vendor Advisory: https://github.com/trusteddomainproject/OpenDMARC/issues/179
Restart Required: Yes
Instructions:
1. Download OpenDMARC 1.4.2 or later from the official repository. 2. Stop OpenDMARC services. 3. Install the updated version following distribution-specific package management procedures. 4. Restart OpenDMARC services.
🔧 Temporary Workarounds
Filter multi-value From headers
linuxConfigure email gateways or filters to reject or sanitize emails with multiple From header values before they reach OpenDMARC.
# Example using Postfix header_checks
/^From:.*,.*/ REJECT Multiple From headers not allowed
🧯 If You Can't Patch
- Implement network segmentation to restrict access to OpenDMARC services from untrusted sources.
- Deploy rate limiting on email processing to reduce impact of potential DoS attacks.
🔍 How to Verify
Check if Vulnerable:
Check OpenDMARC version with 'opendmarc -v' or distribution package manager. Versions 1.4.1 and 1.4.1.1 are vulnerable.Check Version:
opendmarc -v 2>/dev/null || rpm -q opendmarc || dpkg -l | grep opendmarcVerify Fix Applied:
After patching, verify version is 1.4.2 or later and test with sample emails containing multi-value From headers.📡 Detection & Monitoring
Log Indicators:
- Segmentation fault or crash messages in OpenDMARC logs
- Service restart patterns in system logs
Network Indicators:
- Unusual volume of emails with malformed headers
- TCP connections to OpenDMARC port followed by service interruption
SIEM Query:
source="opendmarc.log" AND ("segmentation fault" OR "crash" OR "SIGSEGV")🔗 References
- https://github.com/trusteddomainproject/OpenDMARC/issues/179
- https://github.com/trusteddomainproject/OpenDMARC/pull/178
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2MAT4ZSWPQ5SUTMYCXRXI5SMTWL4AG7E/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VZHZD4WZDYRBB2XVW2EQ4DQ2KYMAGPUO/
- https://github.com/trusteddomainproject/OpenDMARC/issues/179
- https://github.com/trusteddomainproject/OpenDMARC/pull/178
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2MAT4ZSWPQ5SUTMYCXRXI5SMTWL4AG7E/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/VZHZD4WZDYRBB2XVW2EQ4DQ2KYMAGPUO/
