Multiple double free vulnerabilities in the (1) agentsigndata function in agent.c, (2) channelrequest function in channels.c, (3) sshuserauthpubkey function in auth.c, (4) sftpparseattr3 function in sftp.c, and (5) trypublickeyfrom_file function in keyfiles.c in libssh before 0.5.3 allow remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via unspecified vectors.