CVE-2026-42770
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk16th percentile — higher than 16% of all known CVEs
Summary
The vulnerability exists in the EVP_PKEY_derive_set_peer() function, which improperly checks the subgroup membership of the peer key when a DHX (X9.42) key is used. A malicious peer can exploit this flaw to recover the victim's private key after a small number of key exchange attempts.
Risk Assessment
The risk to the organization is the potential for a malicious peer to recover the private key, leading to the compromise of sensitive data. The attack surface is limited to specific deployments, reducing its overall severity.
Recommendation
It is recommended to update the FIPS modules to the latest version and review the configuration of DHX keys to minimize risk. Consideration should also be given to using alternative key exchange methods.
Original NVD description (English source)
Issue summary: When EVP_PKEY_derive_set_peer() is called with a DHX (X9.42) peer key, the peer key is not properly checked for the subgroup membership. Impact summary: A malicious peer which presents an X9.42 key carrying the victim's p and g parameters, a forged q = r (a small prime factor of the cofactor (p−1)/q_local), and a public value Y of order r can recover the victim's private key after a small number of key exchange attempts. When EVP_PKEY_derive_set_peer() is called with a DHX (X9.42) peer key, the subgroup membership check Y^q ≡ 1 (mod p) is performed using the peer's own q parameter, not the local key's q. The peer's domain parameters are then matched against the domain parameters of the private key, but the value of q is not compared. A malicious peer who presents an X9.42 key carrying the victim's p, g, a forged q = r (a small prime factor of the cofactor), and a public value Y of order r passes all checks. The shared secret then takes only r distinct values, leaking priv mod r. Repeating for each small-prime factor of the cofactor and combining via CRT recovers the full private key (Lim–Lee / small-subgroup-confinement attack). The realistic attack surface is narrow: principally CMP deployments with long-lived RA/CA DHX keys and bespoke enterprise or government applications using X9.42 DHX static keys with interactive protocols and therefore this issue was assigned Low severity. The FIPS modules in 4.0, 3.6, 3.5, 3.4, and 3.0 are affected by this issue.