CVE-2020-14145
Description
A flaw was found in OpenSSH in versions 5.7 through 8.3, where an Observable Discrepancy occurs and leads to an information leak in the algorithm negotiation. This flaw allows a man-in-the-middle attacker to target initial connection attempts, where there is no host key for the server that has been cached by the client.
Statement
This is a flaw in OpenSSH, which allows a man in the middle attack to determine, if a client already has prior knowledge of the remote hosts fingerprint. An attacker could use this information to ignore clients, which will show an error message during an man in the middle attack, while new clients can be intercepted without alerting them of the man in the middle attack.
This essentially means that this flaw can help attacker's identify targets an MITM attack. However such a attack would still require the attacker to either have control over DNS or control over the network traffic.
If the network is untrusted, Red Hat suggests the use ssh certificates for even more confidence and less human factor involved or gssapi key exchange, where kerberos is used to verify identity of the server.
Mitigation
Always connect to SSH servers with verified host keys to avoid any possibilities of man-in-the-middle attack.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 5.9 | 5.9 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | High | High |
| Privileges Required | None | None | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | None | None | None |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Understanding the Weakness (CWE)
Confidentiality,Access Control
Technical Impact: Read Application Data; Bypass Protection Mechanism
An attacker can gain access to sensitive information about the system, including authentication information that may allow an attacker to gain access to the system. Other security-relevant information about the operation or internal state of the product may be revealed to an unauthorized actor, such as whether a particular operation was successful or not.
Confidentiality
Technical Impact: Read Application Data
In some cases, discrepancies can be used by attackers to form a side channel. When cryptographic primitives are vulnerable to side-channel attacks, this could be used to reveal unencrypted plaintext in the worst case.
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