BBOT's unarchive module rejects archives containing symlink entries before extraction, but for zip and 7z archives it failed to detect symlinks whose listing carries a DOS-attribute prefix before the unix mode, as produced by legacy versions of p7zip. Such an archive, downloaded and extracted during a scan (for example via filedownload), bypassed the guard and caused an attacker-controlled symlink to be written into the extraction directory. The effect is limited to planting the symlink (its target is not written through), and only hosts using such a legacy p7zip build are affected; current mainline 7-Zip is not.