The connection_state_machine function (connections.c) in lighttpd 1.4.19 and earlier, and 1.5.x before 1.5.0, allows remote attackers to cause a denial of service (active SSL connection loss) by triggering an SSL error, such as disconnecting before a download has finished, which causes all active SSL connections to be lost.

mod_userdir in lighttpd 1.4.18 and earlier, when userdir.path is not set, uses a default of $HOME, which might allow remote attackers to read arbitrary files, as demonstrated by accessing the ~nobody directory.

mod_cgi in lighttpd 1.4.18 sends the source code of CGI scripts instead of a 500 error when a fork failure occurs, which might allow remote attackers to obtain sensitive information.

lighttpd 1.4.18, and possibly other versions before 1.5.0, does not properly calculate the size of a file descriptor array, which allows remote attackers to cause a denial of service (crash) via a large number of connections, which triggers an out-of-bounds access.

Buffer overflow in the fcgi_env_add function in mod_proxy_backend_fastcgi.c in the mod_fastcgi extension in lighttpd before 1.4.18 allows remote attackers to overwrite arbitrary CGI variables and execute arbitrary code via an HTTP request with a long content length, as demonstrated by overwriting the SCRIPT_FILENAME variable, aka a "header overflow."

connections.c in lighttpd before 1.4.16 might accept more connections than the configured maximum, which allows remote attackers to cause a denial of service (failed assertion) via a large number of connection attempts.

mod_access.c in lighttpd 1.4.15 ignores trailing / (slash) characters in the URL, which allows remote attackers to bypass url.access-deny settings.

request.c in lighttpd 1.4.15 allows remote attackers to cause a denial of service (daemon crash) by sending an HTTP request with duplicate headers, as demonstrated by a request containing two Location header lines, which results in a segmentation fault.

mod_auth (http_auth.c) in lighttpd before 1.4.16 allows remote attackers to cause a denial of service (daemon crash) via unspecified vectors involving (1) a memory leak, (2) use of md5-sess without a cnonce, (3) base64 encoded strings, and (4) trailing whitespace in the Auth-Digest header.

lighttpd 1.4.15, when run on 32 bit platforms, allows remote attackers to cause a denial of service (daemon crash) via unspecified vectors involving the use of incompatible format specifiers in certain debugging messages in the (1) mod_scgi, (2) mod_fastcgi, and (3) mod_webdav modules.