An improper neutralization of special elements vulnerability was identified in GitHub Enterprise Server that allowed an attacker with push access to a repository to achieve remote code execution on the instance. During a git push operation, user-supplied push option values were not properly sanitized before being included in internal service headers. Because the internal header format used a delimiter character that could also appear in user input, an attacker could inject additional metadata fields through crafted push option values. This vulnerability was reported via the GitHub Bug Bounty program and has been fixed in GitHub Enterprise Server versions 3.14.24, 3.15.19, 3.16.15, 3.17.12, 3.18.6 and 3.19.3.
Weakness
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
Affected Software
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Enterprise_server | Github | * | 3.14.24 (excluding) |
| Enterprise_server | Github | 3.15.0 (including) | 3.15.19 (excluding) |
| Enterprise_server | Github | 3.16.0 (including) | 3.16.15 (excluding) |
| Enterprise_server | Github | 3.17.0 (including) | 3.17.12 (excluding) |
| Enterprise_server | Github | 3.18.0 (including) | 3.18.6 (excluding) |
| Enterprise_server | Github | 3.19.0 (including) | 3.19.3 (excluding) |
Extended Description
Many protocols and products have their own custom command language. While OS or shell command strings are frequently discovered and targeted, developers may not realize that these other command languages might also be vulnerable to attacks.
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.
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/136.html
- https://cwe.mitre.org/data/definitions/15.html
- https://cwe.mitre.org/data/definitions/183.html
- https://cwe.mitre.org/data/definitions/248.html
- https://cwe.mitre.org/data/definitions/40.html
- https://cwe.mitre.org/data/definitions/43.html
- https://cwe.mitre.org/data/definitions/75.html
- https://cwe.mitre.org/data/definitions/76.html
References
- https://docs.github.com/en/enterprise-server@3.14/admin/release-notes#3.14.24
- https://docs.github.com/en/enterprise-server@3.15/admin/release-notes#3.15.19
- https://docs.github.com/en/enterprise-server@3.16/admin/release-notes#3.16.15
- https://docs.github.com/en/enterprise-server@3.17/admin/release-notes#3.17.12
- https://docs.github.com/en/enterprise-server@3.18/admin/release-notes#3.18.6
- https://docs.github.com/en/enterprise-server@3.19/admin/release-notes#3.19.3