Putty pscp <= 0.66 - Stack Buffer Overwrite

Credit: tintinweb
Risk: High
Local: No
Remote: Yes
CWE: CWE-121

CVSS Base Score: 7.5/10
Impact Subscore: 6.4/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Partial

Source: https://github.com/tintinweb/pub/tree/master/pocs/cve-2016-2563 Author: <github.com/tintinweb> Date: Feb 20th, 2016 Name: putty Vendor: sgtatham - http://www.chiark.greenend.org.uk/~sgtatham/putty/ Version: 0.59 [3] (~9 years ago) <= affected <= 0.66 Platform(s): win/nix Technology: c Vuln Classes: stack buffer overwrite (CWE-121) Origin: remote Min. Privs.: post auth CVE: CVE-2016-2563 Summary The putty SCP command-line utility (pscp) is missing a bounds-check for a stack buffer when processing the SCP-SINK file-size response to a SCP download request. This may allow a malicious server to overwrite the stack buffer within the client- application potentially leading to remote code execution. PoC attached. patch attached. Besides that, two minor issues have been reported in putty packet handling: DoS condition in the parsing of SSH-Strings that lead to a nullptr read. (connect putty to poc.py and type x11exploit to trigger one of multiple occurrence of a crash, also works with x11forwarding disabled in putty) DoS condition in the handling of unrequested forwarded-tcpip channels open requests that lead to a nullptr read. (connect putty to poc.py and type forwardedtcpipcrash to trigger crash) Details The vulnerable code is located in pscp.c [4] line 1498 (HEAD) and is based on an unbound sscanf string format descriptor storing an arbitrary length string in a 40byte fixed size stack buffer sizestr[40].



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