Unrar VMSF_DELTA Arbitrary Memory Write

It appears that the VMSF_DELTA memory corruption that was reported to Sophos AV in 2012 (and fixed there) was actually inherited from upstream unrar. For unknown reasons, whoever fixed the bug did not report this to upstream unrar, and the bug seems to have persisted there to this day.
Source: Unrar VMSF_DELTA Arbitrary Memory Write