Microsoft Exchange Server: information disclosure flaw under attack

What is affected

Microsoft Exchange Server is mostly run by companies, schools and public bodies, not on home computers. You are unlikely to have it yourself, but organisations that hold your data may. Breaches that start with flaws like this one are how personal data ends up leaked.

Microsoft Exchange Server contains an information disclosure vulnerability that allows for remote code execution.

What an attacker can do

This is a information disclosure flaw. It lets an attacker read data they are not supposed to see, such as memory contents, credentials or internal files. It is often the first step of a larger attack.

How it is reached

Over the internet or network

Access the attacker needs

An administrator account

Does the victim have to do something?

No, works without the victim doing anything

What to do

1. At home: nothing to install. Keep your own devices updated and use a different password for every service, so that a breach at one organisation does not open your other accounts.
2. If you administer Microsoft Exchange Server at work: apply the vendor's fix or mitigation now and review logs for signs of compromise, because the flaw was being exploited before it was listed.
3. If the product is past its support date and no fix exists, take it off the internet or retire it.

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Vendor advisories and fixes

• msrc.microsoft.commsrc.microsoft.com/update-guide/en-US/advisory/CVE-2021-31196

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on August 21, 2024, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by September 11, 2024, a deadline that has already passed. That deadline does not bind anyone else, but it shows how seriously the agency rates it.

The EPSS model estimates a 54% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99% of all scored vulnerabilities.

Its CVSS severity score is 7.2 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Microsoft Exchange Server Remote Code Execution Vulnerability