Ruby before 2.4.3 allows Net::FTP command injection. Net::FTP#get, getbinaryfile, gettextfile, put, putbinaryfile, and puttextfile use Kernel#open to open a local file. If the localfile argument starts with the "|" pipe character, the command following the pipe character is executed. The default value of localfile is File.basename(remotefile), so malicious FTP servers could cause arbitrary command execution.

The decode method in the OpenSSL::ASN1 module in Ruby before 2.2.8, 2.3.x before 2.3.5, and 2.4.x through 2.4.1 allows attackers to cause a denial of service (interpreter crash) via a crafted string.

The Basic authentication code in WEBrick library in Ruby before 2.2.8, 2.3.x before 2.3.5, and 2.4.x through 2.4.1 allows remote attackers to inject terminal emulator escape sequences into its log and possibly execute arbitrary commands via a crafted user name.

Ruby before 2.4.2, 2.3.5, and 2.2.8 is vulnerable to a malicious format string which contains a precious specifier (*) with a huge minus value. Such situation can lead to a buffer overrun, resulting in a heap memory corruption or an information disclosure from the heap.

The URI.decode_www_form_component method in Ruby before 1.9.2-p330 allows remote attackers to cause a denial of service (catastrophic regular expression backtracking, resource consumption, or application crash) via a crafted string.

Ruby through 2.2.7, 2.3.x through 2.3.4, and 2.4.x through 2.4.1 can expose arbitrary memory during a JSON.generate call. The issues lies in using strdup in ext/json/ext/generator/generator.c, which will stop after encountering a '\0' byte, returning a pointer to a string of length zero, which is not the length stored in space_len.

The parser_yyerror function in the UTF-8 parser in Ruby 2.4.1 allows attackers to cause a denial of service (invalid write or read) or possibly have unspecified other impact via a crafted Ruby script, related to the parser_tokadd_utf8 function in parse.y. NOTE: this might have security relevance as a bypass of a $SAFE protection mechanism.

Net::SMTP in Ruby before 2.4.0 is vulnerable to SMTP command injection via CRLF sequences in a RCPT TO or MAIL FROM command, as demonstrated by CRLF sequences immediately before and after a DATA substring.

An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds write in onigenc_unicode_get_case_fold_codes_by_str() occurs during regular expression compilation. Code point 0xFFFFFFFF is not properly handled in unicode_unfold_key(). A malformed regular expression could result in 4 bytes being written off the end of a stack buffer of expand_case_fold_string() during the call to onigenc_unicode_get_case_fold_codes_by_str(), a typical stack buffer overflow.

An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A SIGSEGV occurs in left_adjust_char_head() during regular expression compilation. Invalid handling of reg->dmax in forward_search_range() could result in an invalid pointer dereference, normally as an immediate denial-of-service condition.