# Exploit Title: Boa Web Server v0.94.14 - Authentication Bypass #Date: 19-11-2022 # Exploit Author: George Tsimpidas # Vendor: https://github.com/gpg/boa # CVE: N/A # Tested on: Debian 5.18.5 Description : Boa Web Server Versions from 0.94.13 - 0.94.14 fail to validate the correct security constraint on the HEAD http method allowing everyone to bypass the Basic Authorization Mechanism. Culprit : if (!memcmp(req->logline, "GET ", 4)) req->method = M_GET; else if (!memcmp(req->logline, "HEAD ", 5)) /* head is just get w/no body */ req->method = M_HEAD; else if (!memcmp(req->logline, "POST ", 5)) req->method = M_POST; else { log_error_doc(req); fprintf(stderr, "malformed request: \"%s\"\n", req->logline); send_r_not_implemented(req); return 0; } The req->method = M_HEAD; is being parsed directly on the response.c file, looking at how the method is being implemented for one of the response codes : /* R_NOT_IMP: 505 */ void send_r_bad_version(request * req) { SQUASH_KA(req); req->response_status = R_BAD_VERSION; if (!req->simple) { req_write(req, "HTTP/1.0 505 HTTP Version Not Supported\r\n"); print_http_headers(req); req_write(req, "Content-Type: " HTML "\r\n\r\n"); /* terminate header */ } if (req->method != M_HEAD) { req_write(req, "505 HTTP Version Not Supported\n" "

505 HTTP Version Not Supported

\nHTTP versions " "other than 0.9 and 1.0 " "are not supported in Boa.\n

Version encountered: "); req_write(req, req->http_version); req_write(req, "

\n"); } req_flush(req); } Above code condition indicates that if (req->method != M_HEAD) therefore if the the requested method does not equal to M_HEAD then req_write(req, "505 HTTP Version Not Supported\n" "

505 HTTP Version Not Supported

\nHTTP versions " "other than 0.9 and 1.0 " "are not supported in Boa.\n

Version encountered: "); req_write(req, req->http_version); req_write(req, "

\n"); } So if the method actually contains the http method of HEAD it's being passed for every function that includes all the response code methods.