In Network Security Services (NSS) before 3.46, several cryptographic primitives had missing length checks. In cases where the application calling the library did not perform a sanity check on the inputs it could result in a crash due to a buffer overflow.
When encrypting with a block cipher, if a call to NSC_EncryptUpdate was made with data smaller than the block size, a small out of bounds write could occur. This could have caused heap corruption and a potentially exploitable crash. This vulnerability affects Thunderbird < 68.3, Firefox ESR < 68.3, and Firefox < 71.