census ID: census-2009-0003 URL: http://census-labs.com/news/2009/12/02/corehttp-web-server/ CVE ID: CVE-2009-3586 Affected Products: CoreHTTP web server versions <= 0.5.3.1. Class: Improper Input Validation (CWE-20), Failure to Constrain Operations within the Bounds of a Memory Buffer (CWE-119) Remote: Yes Discovered by: Patroklos Argyroudis We have discovered a remotely exploitable "improper input validation" vulnerability in the CoreHTTP web server that leads to an off-by-one stack buffer overflow. The vulnerability can lead to denial of service attacks against the web server and potentially to the remote execution of arbitrary code with the privileges of the user running the server. Details CoreHTTP (http://corehttp.sourceforge.net/) is a minimalist web server focusing on speed and size. More information about its features can be found at http://corehttp.sourceforge.net/man.html. CoreHTTP (up to and including version 0.5.3.1) employs an insufficient input validation method for handling HTTP requests with invalid method names and URIs. Specifically, the vulnerability is an off-by-one buffer overflow in the sscanf() call at file src/http.c line numbers 45 and 46: 45: sscanf(parentsprock->buffer, 46: "%" PATHSIZE_S "[A-Za-z] %" PATHSIZE_S "s%*[ \t\n]", req, url); The buffers req and url are declared to be of size 256 bytes (PATHSIZE) and the sscanf() call writes 256 bytes (PATHSIZE_S) to these buffers without NULL terminating them. Note that this is not vulnerability CVE-2007-4060 in which the same sscanf() call contained no bounds check at all. This vulnerability can lead to denial of service attacks against the CoreHTTP web server and potentially to the remote execution of arbitrary code with the privileges of the user running the server. We have developed a proof-of-concept exploit to demonstrate the vulnerability: http://census-labs.com/media/corex.txt For the time being, one may use the following workaround to address this issue, until an official fix is released by the author: http://census-labs.com/media/corehttp-0.5.3.1-patch.txt -- Patroklos Argyroudis http://www.census-labs.com/