CVE-2024-48938

What it actually does

The flaw permits a regular expression denial of service (ReDoS) condition when parsing email content containing HTML copied from Microsoft Word, resulting in excessive CPU consumption that blocks the email parsing process.

Why it matters to the business

Email processing services can become slow or unresponsive, disrupting communication flows and operational workflows until resources are freed or the affected component is restarted; low exploit likelihood reduces immediate urgency but still warrants patching given the published fix.

How an attack unfolds

An attacker crafts an email embedding HTML from Microsoft Word that triggers catastrophic backtracking in the regex engine used for content parsing, causing sustained high CPU usage that stalls the parser and denies service to legitimate email handling.

How to fix it

Upgrade the affected Mattermost component to version 9.1.5+incompatible or later to resolve the ReDoS condition in email parsing.

How to confirm the fix worked

Confirm the installed version meets or exceeds the fixed release, then replay sample emails with Microsoft Word-derived HTML to verify CPU usage remains bounded during parsing.

Typical attack path

1. Craft an email containing specially structured HTML copied from Microsoft Word
2. Deliver the email to the target system via normal channels
3. Trigger the email content parsing routine
4. Induce resource exhaustion that blocks further processing

How to detect it

Review email processing logs and system performance counters for prolonged high CPU intervals coinciding with inbound message handling; no known in-the-wild exploitation artifacts are available.

What your security team should do

• Apply the published fixed version promptly to eliminate the parsing flaw
• Monitor CPU and parsing queue metrics for anomalous spikes tied to email ingestion
• Consider rate-limiting or sandboxing of inbound email content until upgrades are complete