CVE-2017-6865

A vulnerability has been identified in Primary Setup Tool (PST) (All versions < V4.2 HF1), SIMATIC Automation Tool (All versions < V3.0), SIMATIC NET PC-Software (All versions < V14 SP1), SIMATIC PCS 7 V8.1 (All versions), SIMATIC PCS 7 V8.2 (All versions < V8.2 SP1), SIMATIC STEP 7 (TIA Portal) V13 (All versions < V13 SP2), SIMATIC STEP 7 (TIA Portal) V14 (All versions < V14 SP1), SIMATIC STEP 7 V5.X (All versions < V5.6), SIMATIC WinAC RTX 2010 SP2 (All versions), SIMATIC WinAC RTX F 2010 SP2 (All versions), SIMATIC WinCC (TIA Portal) V13 (All versions < V13 SP2), SIMATIC WinCC (TIA Portal) V14 (All versions < V14 SP1), SIMATIC WinCC V7.2 and prior (All versions), SIMATIC WinCC V7.3 (All versions < V7.3 Update 15), SIMATIC WinCC V7.4 (All versions < V7.4 SP1 Upd1), SIMATIC WinCC flexible 2008 (All versions < flexible 2008 SP5), SINAUT ST7CC (All versions installed in conjunction with SIMATIC WinCC < V7.3 Update 15), SINEMA Server (All versions < V14), SINUMERIK 808D Programming Tool (All versions < V4.7 SP4 HF2), SMART PC Access (All versions < V2.3), STEP 7 - Micro/WIN SMART (All versions < V2.3), Security Configuration Tool (SCT) (All versions < V5.0). Specially crafted PROFINET DCP broadcast packets sent to the affected products on a local Ethernet segment (Layer 2) could cause a Denial-of-Service condition of some services. The services require manual restart to recover.

Weakness

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

Affected Software

Extended Description

Input validation is a frequently-used technique for checking potentially dangerous inputs in order to ensure that the inputs are safe for processing within the code, or when communicating with other components. Input can consist of:

Data can be simple or structured. Structured data can be composed of many nested layers, composed of combinations of metadata and raw data, with other simple or structured data. Many properties of raw data or metadata may need to be validated upon entry into the code, such as:

Implied or derived properties of data must often be calculated or inferred by the code itself. Errors in deriving properties may be considered a contributing factor to improper input validation.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
• Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
• Inputs should be decoded and canonicalized to the application’s current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control.
• Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.

Related Attack Patterns

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References

• https://cert-portal.siemens.com/productcert/pdf/ssa-275839.pdf
• https://www.securityfocus.com/bid/98366
• https://cert-portal.siemens.com/productcert/pdf/ssa-275839.pdf
• https://www.securityfocus.com/bid/98366