Horizon Alert
Summary of the vulnerability and why it matters
This vulnerability affects wolfSSH, an SSH library, by allowing an attacker to substitute a host key with a different one during a connection. This could mislead a client into trusting an incorrect key, potentially enabling man-in-the-middle attacks if certain client-side security checks are not robust. The primary concern is confirming if this specific library is in use and if the conditions for exploitation exist within your environment.
- SSH key validation weakness exploited.
- Matters if using SSH with weak key checks.
- Confirm relevance and exposure are key.
Attack Path
How an attacker could exploit the issue
An attacker with the ability to intercept network traffic could trick an SSH client into connecting to them by impersonating a legitimate server. This is achieved by presenting a forged host key during the connection setup. If the client's host key validation is not robust, it will import the attacker's key, allowing the attacker to proceed with the connection and potentially gain unauthorized access or eavesdrop on communications.
- Requires man-in-the-middle network access.
- Client must improperly validate host keys.
- Risk of unauthorized access and eavesdropping.
Live Threat
Current exploitation, exposure, and threat context
When supported by the advisory, an attacker in a network man-in-the-middle position could trick a client into accepting a forged host key, potentially leading to compromised connection integrity. This occurs because the SSH library does not properly validate the Elliptic Curve Digital Signature Algorithm (ECDSA) curve identifier in the host key blob against the negotiated algorithm during the key exchange. Exploitation is contingent on the client having a lax public key check callback.
- Host keys could be compromised.
- Attacker substitutes a forged host key blob.
- Malicious connections may be accepted.
Operational Fix
Recommended remediation, mitigation, and detection steps
The SSH library's handling of ECDSA curve identifiers in host key verification presents a risk that requires immediate attention from teams managing SSH infrastructure and client applications. The first practical step is to identify all instances of the affected SSH library, determine their network exposure, and pinpoint the accountable system owners. This will allow for a risk-based remediation plan.
- Identify SSH client and server deployments.
- Verify public key verification logic.
- Plan remediation based on exposure.
