Security Vulnerabilities fixed in Firefox 101 — Mozilla

A malicious website could have learned the size of a cross-origin resource that supported Range requests.
A malicious webpage could have caused an out-of-bounds write in WebGL, leading to memory corruption and a potentially exploitable crash.
When exiting fullscreen mode, an iframe could have confused the browser about the current state of fullscreen, resulting in potential user confusion or spoofing attacks.
When downloading files on Windows, the % character was not escaped, which could have lead to a download incorrectly being saved to attacker-influenced paths that used variables such as %HOMEPATH% or %APPDATA%.This bug only affects Firefox for Windows. Other operating systems are unaffected.
On arm64, WASM code could have resulted in incorrect assembly generation leading to a register allocation problem, and a potentially exploitable crash.
A crafted CMS message could have been processed incorrectly, leading to an invalid memory read, and potentially further memory corruption.
An attacker could have exploited a timing attack by sending a large number of allowCredential entries and detecting the difference between invalid key handles and cross-origin key handles. This could have led to cross-origin account linking in violation of WebAuthn goals.
Firefox’s HTML parser did not correctly interpret HTML comment tags, resulting in an incongruity with other browsers. This could have been used to escape HTML comments on pages that put user-controlled data in them.
An attacker could have injected CSS into stylesheets accessible via internal URIs, such as resource:, and in doing so bypass a page’s Content Security Policy.
If array shift operations are not used, the Garbage Collector may have become confused about valid objects.
An attacker could have caused an uninitialized variable on the stack to be mistakenly freed, causing a potentially exploitable crash.
Mozilla developers Andrew McCreight, Nicolas B. Pierron, and the Mozilla Fuzzing Team reported memory safety bugs present in Firefox 100 and Firefox ESR 91.9. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.
Mozilla developers Gabriele Svelto, Timothy Nikkel, Randell Jesup, Jon Coppeard, and the Mozilla Fuzzing Team reported memory safety bugs present in Firefox 100. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.