Mozilla Firefox postMessage DOM Mitigation Bypass (CVE20266755)
CVE-2026-6755 Published on April 21, 2026
Mitigation bypass in the DOM: postMessage component
Mitigation bypass in the DOM: postMessage component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.
Vulnerability Analysis
CVE-2026-6755 can be exploited with network access, and requires small amount of user privileges. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
What is a Session Riding Vulnerability?
The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request. When a web server is designed to receive a request from a client without any mechanism for verifying that it was intentionally sent, then it might be possible for an attacker to trick a client into making an unintentional request to the web server which will be treated as an authentic request. This can be done via a URL, image load, XMLHttpRequest, etc. and can result in exposure of data or unintended code execution.
CVE-2026-6755 has been classified to as a Session Riding vulnerability or weakness.
Products Associated with CVE-2026-6755
stack.watch emails you whenever new vulnerabilities are published in Mozilla Firefox or Mozilla Thunderbird. Just hit a watch button to start following.
Affected Versions
Mozilla Firefox:- Version 150, <= * is unaffected.
- Version 150, <= * is unaffected.