user/libebml: CVE-2021-3405: heap overflow bug in libebml before 1.4.2

CVE-2021-3405: In libebml before 1.4.2, a heap overflow bug exists in the implementation of EbmlString::ReadData and EbmlUnicodeString::ReadData.

added SECURITY label

changed title from user/libebml: heap overflow bug in libebml before 1.4.2 to user/libebml: CVE-2021-3405: heap overflow bug in libebml before 1.4.2

mentioned in merge request !708 (merged)

closed with merge request !708 (merged)

mentioned in commit 7f11dddb

mentioned in commit 7a299476