The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode(xn–example-.com) incorrectly returns the name example.com rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject example.com but permit xn–example-.com. If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name example.com.
Weakness
The product receives an input value that is used as a resource identifier or other type of reference, but it does not validate or incorrectly validates that the input is equivalent to a potentially-unsafe value.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Net | Golang | * | 0.55.0 (excluding) |
| Red Hat Advanced Cluster Security for Kubernetes 4.10 | RedHat | advanced-cluster-security/rhacs-main-rhel8:1781686458 | * |
| Red Hat Advanced Cluster Security for Kubernetes 4.9 | RedHat | advanced-cluster-security/rhacs-main-rhel8:1781686446 | * |
| Red Hat Hardened Images | RedHat | golang1-25-main-1.25.11-2.hum1 | * |
| Red Hat Hardened Images | RedHat | golang1-26-main-1.26.4-2.hum1 | * |
| Golang-golang-x-net-dev | Ubuntu | esm-apps/bionic | * |
| Golang-golang-x-net-dev | Ubuntu | esm-apps/focal | * |
Extended Description
Attackers can sometimes bypass input validation schemes by finding inputs that appear to be safe, but will be dangerous when processed at a lower layer or by a downstream component. For example, a simple XSS protection mechanism might try to validate that an input has no “” tags using case-sensitive matching, but since HTML is case-insensitive when processed by web browsers, an attacker could inject “” and trigger XSS.
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.