title: TLS 1.3 client issue handling malicious server when not including a KSE and PSK extension
description: If a TLS 1.3 client gets neither a PSK (pre shared key) extension nor a KSE (key share extension) when connecting to a malicious server, a default predictable buffer gets used for the IKM (Input Keying Material) value when generating the session master secret. Using a potentially known IKM value when generating the session master secret key compromises the key generated, allowing an eavesdropper to reconstruct it and potentially allowing access to or meddling with message contents in the session. This issue does not affect client validation of connected servers, nor expose private key information, but could result in an insecure TLS 1.3 session when not controlling both sides of the connection. wolfSSL recommends that TLS 1.3 client side users update the version of wolfSSL used.
problem types: CWE-20 Improper Input Validation
affected:
{
defaultStatus: unaffected
product: wolfSSL
vendor: wolfSSL
versions:
lessThanOrEqual: 5.6.0, status: affected, version: 3.14.0, versionType: release bundle
}
metrics:
cvssV3_1: [
attackComplexity: LOW
attackVector: NETWORK
availabilityImpact: HIGH
baseScore: 9.1
baseSeverity: CRITICAL
confidentialityImpact: HIGH
integrityImpact: HIGH
privilegesRequired: HIGH
scope: CHANGED
userInteraction: NONE
vectorString: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
version: 3.1
]
format: CVSS
scenarios: GENERAL
solutions:
Fixed in the following GitHub pull request  https://github.com/wolfSSL/wolfssl/pull/6412 https://github.com/wolfSSL/wolfssl/pull/6412