`EncryptingOutputStream` was susceptible to exposing uninitialized data. This issue could only be abused in order to write data to a local disk which may have implications for private browsing mode. This vulnerability affects Firefox ESR < 115.6 and Firefox < 121.
https://www.mozilla.org/security/advisories/mfsa2023-56/
https://www.mozilla.org/security/advisories/mfsa2023-54/
https://www.debian.org/security/2023/dsa-5581
https://security.gentoo.org/glsa/202401-10
https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html