CVE-2018-5131 Explained : Impact and Mitigation

A vulnerability in the "fetch()" API of Firefox ESR and Firefox versions could allow access to locally cached data of websites under specific conditions.

Understanding CVE-2018-5131

In specific situations, the "fetch()" API has the potential to retrieve temporary local versions of resources that were originally sent with a cache header specifying "no-store" or "no-cache" instead of fetching a copy from the network as intended. This impacts Firefox ESR version 52.7 and Firefox version 59 and older.

What is CVE-2018-5131?

Under certain circumstances, the "fetch()" API can return transient local copies of resources that were sent with a "no-store" or "no-cache" cache header instead of downloading a copy from the network as it should. This can result in previously stored, locally cached data of a website being accessible to users if they share a common profile while browsing.

The Impact of CVE-2018-5131

Users with shared profiles may access locally cached data of websites.

Technical Details of CVE-2018-5131

The technical details of the vulnerability are as follows:

Vulnerability Description

The vulnerability allows the "fetch()" API to return cached copies of resources marked with "no-store" or "no-cache" headers, potentially exposing locally cached data.

Affected Systems and Versions

Products: Firefox ESR, Firefox
Versions: Firefox ESR < 52.7, Firefox < 59

Exploitation Mechanism

The vulnerability occurs when the "fetch()" API retrieves temporary local versions of resources instead of fetching from the network, exposing cached data.

Mitigation and Prevention

To address CVE-2018-5131, consider the following steps:

Immediate Steps to Take

Update Firefox ESR to version 52.7 or newer.
Update Firefox to version 59 or newer.
Avoid sharing profiles while browsing.

Long-Term Security Practices

Regularly update browsers to the latest versions.
Educate users on the risks of shared profiles.

Patching and Updates

Apply security patches provided by Mozilla.