Atlassian Confluence Server and Data Center: file access flaw under attack

What is affected

Atlassian Confluence Server and Data Center 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.

Atlassian Confluence Server and Data Center contain a path traversal vulnerability in the downloadallattachments resource that may allow a privileged, remote attacker to write files. Exploitation can lead to remote code execution.

What an attacker can do

This is a file access flaw. It lets an attacker read or write files they should never reach, such as configuration files that hold passwords, or upload a malicious file that the system then runs.

How it is reached

Over the internet or network

Access the attacker needs

A basic user 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 Atlassian Confluence Server and Data Center 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 updates per vendor instructions.

How urgent is it

CISA added this vulnerability to its Known Exploited Vulnerabilities catalogue on November 3, 2021, which means there is reliable evidence of attacks in the wild. US federal agencies must fix it by May 3, 2022, 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 97% probability that this flaw will be exploited somewhere in the next 30 days. That is higher than 99.9% of all scored vulnerabilities.

Its CVSS severity score is 8.8 out of 10 (high), as recorded in the US National Vulnerability Database.

Technical description

Confluence Server and Data Center had a path traversal vulnerability in the downloadallattachments resource. A remote attacker who has permission to add attachments to pages and / or blogs or to create a new space or a personal space or who has 'Admin' permissions for a space can exploit this path traversal vulnerability to write files to arbitrary locations which can lead to remote code execution on systems that run a vulnerable version of Confluence Server or Data Center. All versions of Confluence Server from 2.0.0 before 6.6.13 (the fixed version for 6.6.x), from 6.7.0 before 6.12.4 (the fixed version for 6.12.x), from 6.13.0 before 6.13.4 (the fixed version for 6.13.x), from 6.14.0 before 6.14.3 (the fixed version for 6.14.x), and from 6.15.0 before 6.15.2 are affected by this vulnerability.