CVE-2026-42770

Publication date 9 June 2026

Last updated 18 June 2026

Ubuntu priority

Low

Why this priority?

Cvss 3 Severity Score

3.7 · Low

Score breakdown

Description

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.

Read the notes from the security team

Why is this CVE low priority?

OpenSSL developers have rated this as being low severity

Learn more about Ubuntu priority

Status

Package Ubuntu Release Status
edk2 26.04 LTS resolute
Needs evaluation
25.10 questing
Needs evaluation
24.04 LTS noble
Needs evaluation
22.04 LTS jammy
Not affected
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
nodejs 26.04 LTS resolute
Not affected
25.10 questing
Not affected
24.04 LTS noble
Not affected
22.04 LTS jammy
Vulnerable
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
14.04 LTS trusty
Not affected
openssl 26.04 LTS resolute
Fixed 3.5.5-1ubuntu3.2
25.10 questing
Fixed 3.5.3-1ubuntu3.4
24.04 LTS noble
Fixed 3.0.13-0ubuntu3.11
22.04 LTS jammy
Fixed 3.0.2-0ubuntu1.25
20.04 LTS focal
Not affected
18.04 LTS bionic
Not affected
16.04 LTS xenial
Not affected
14.04 LTS trusty
Not affected
openssl-fips 26.04 LTS resolute Not in release
25.10 questing Not in release
24.04 LTS noble Not in release
22.04 LTS jammy Not in release
openssl1.0 26.04 LTS resolute Not in release
25.10 questing Not in release
24.04 LTS noble Not in release
22.04 LTS jammy Not in release
18.04 LTS bionic
Not affected

Notes

mdeslaur

edk2 in jammy embeds OpenSSL 1.1.1j edk2 in noble embeds OpenSSL 3.0.9 edk2 in plucky embeds OpenSSL 3.4.0 edk2 in questing embeds OpenSSL 3.4.0 nodejs in jammy embeds OpenSSL 1.1.1m OpenSSL 4.0, 3.6, 3.5, 3.4, and 3.0 are vulnerable to this issue.

Severity score breakdown

CVSS version: CVSS v3.0

Base score 3.7 · Low

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

References

Related Ubuntu Security Notices (USN)

Other references

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