CVE-2021-27408

The affected product is vulnerable to an out-of-bounds read, which can cause information leakage leading to arbitrary code execution if chained to the out-of-bounds write vulnerability on the Welch Allyn medical device management tools (Welch Allyn Service Tool: versions prior to v1.10, Welch Allyn Connex Device Integration Suite – Network Connectivity Engine (NCE): versions prior to v5.3, Welch Allyn Software Development Kit (SDK): versions prior to v3.2, Welch Allyn Connex Central Station (CS): versions prior to v1.8.6, Welch Allyn Service Monitor: versions prior to v1.7.0.0, Welch Allyn Connex Vital Signs Monitor (CVSM): versions prior to v2.43.02, Welch Allyn Connex Integrated Wall System (CIWS): versions prior to v2.43.02, Welch Allyn Connex Spot Monitor (CSM): versions prior to v1.52, Welch Allyn Spot Vital Signs 4400 Device (Spot 4400) / Welch Allyn Spot 4400 Vital Signs Extended Care Device: versions prior to v1.11.00).

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

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.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://us-cert.cisa.gov/ics/advisories/icsma-21-152-01