CVE-2024-23184

What it actually does

Excessive CPU consumption during parsing of a large number of email address headers (From, To, Cc, Bcc), with 100k headers taking 12 seconds and 500k taking 18 minutes.

Why it matters to the business

External attackers can trigger resource exhaustion leading to email service outages and degraded system availability.

How an attack unfolds

An attacker sends a specially crafted email containing hundreds of thousands of address headers to a vulnerable email server, causing the header parsing routine to consume excessive CPU time and resulting in denial of service.

How to fix it

Implement restrictions on the number of address headers at the MTA layer preceding the affected component; upgrade to a version that addresses the parsing inefficiency.

How to confirm the fix worked

Test header parsing performance with controlled high-volume address header messages and monitor CPU utilization before and after applying restrictions or updates.

Typical attack path

1. Craft an email message containing 100k or more address headers
2. Deliver the message via SMTP to the target system
3. Trigger the address header parsing code path
4. Sustain or repeat the attack to prolong CPU exhaustion and outage

How to detect it

Review mail server logs for incoming messages with unusually high header counts and correlate with spikes in CPU usage on the parsing process.

What your security team should do

• Deploy MTA-level header count limits immediately
• Prioritize patching the affected component to the fixed release
• Add monitoring for anomalous CPU spikes during email ingestion