Mozilla · Firefox Esr · CVE-2017-7807
**Name of the Vulnerable Software and Affected Versions**
Thunderbird versions prior to 52.3
Firefox ESR versions prior to 52.3
Firefox versions prior to 55
**Description**
The issue is related to a mechanism that uses AppCache to hijack a URL in a domain. This is achieved by serving files from a sub-path on the domain using fallback. The problem stems from weaknesses in the Application Cache mechanism, which can be exploited by a remote attacker to substitute a domain using the FALLBACK section of the manifest files of isolated sources.
**Recommendations**
For Thunderbird versions prior to 52.3, update to version 52.3 or later.
For Firefox ESR versions prior to 52.3, update to version 52.3 or later.
For Firefox versions prior to 55, update to version 55 or later.