An issue was discovered in OpenVPN 2.4.x before 2.4.9. An attacker can inject a data channel v2 (P_DATA_V2) packet using a victims peer-id. Normally such packets are dropped, but if this packet arrives before the data channel crypto parameters have been initialized, the victims connection will be dropped. This requires careful timing due to the small time window (usually within a few seconds) between the victim client connection starting and the server PUSH_REPLY response back to the client. This attack will only work if Negotiable Cipher Parameters (NCP) is in use.
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Openvpn | Openvpn | 2.4.0 (including) | 2.4.9 (excluding) |
| Openvpn | Ubuntu | bionic | * |
| Openvpn | Ubuntu | eoan | * |
| Openvpn | Ubuntu | esm-infra/bionic | * |
| Openvpn | Ubuntu | esm-infra/focal | * |
| Openvpn | Ubuntu | focal | * |
| Openvpn | Ubuntu | trusty | * |
| Openvpn | Ubuntu | upstream | * |
A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.