CVE-2020-26958 : Security Advisory and Response

Firefox did not block execution of scripts with incorrect MIME types when the response was intercepted and cached through a ServiceWorker, potentially leading to security vulnerabilities.

Understanding CVE-2020-26958

This CVE affects Firefox, Firefox ESR, and Thunderbird versions below specific thresholds.

What is CVE-2020-26958?

This vulnerability arises from the failure of Firefox to restrict the execution of scripts with incorrect MIME types when cached through a ServiceWorker, posing risks of cross-site script inclusion or Content Security Policy bypass.

The Impact of CVE-2020-26958

The vulnerability affects Firefox versions below 83, Firefox ESR versions below 78.5, and Thunderbird versions below 78.5.

Technical Details of CVE-2020-26958

This section delves into the technical aspects of the CVE.

Vulnerability Description

Firefox's inability to block scripts with incorrect MIME types cached through a ServiceWorker could result in security loopholes.

Affected Systems and Versions

Firefox versions below 83
Firefox ESR versions below 78.5
Thunderbird versions below 78.5

Exploitation Mechanism

The vulnerability can be exploited by intercepting requests through ServiceWorkers without MIME type restrictions.

Mitigation and Prevention

Protecting systems from CVE-2020-26958 is crucial. Here are some steps to consider:

Immediate Steps to Take

Update affected software to versions above the specified thresholds.
Monitor security advisories for related patches and updates.

Long-Term Security Practices

Implement strict MIME type checking in web applications.
Regularly review and update Content Security Policies.

Patching and Updates

Apply patches provided by Mozilla promptly to address the vulnerability.