CVE-2026-42770 | FFC-DH Peer Validation Uses Attacker-Supplied q

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.

Published: 2026-06-09 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-42770 is rated Low Risk (20.5/100): CVSS Low severity, with low exploitation likelihood (EPSS 0.25%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-42770

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-18 0.25% 0.25% +0.00%
2 2026-06-15 0.01% 0.25% +0.24%
3 2026-06-10 — 0.01% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-42770

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
3.7 3.1 LOW
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 1.4 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-42770

GitHub Security Advisory for CVE-2026-42770

GHSA-3cxm-476w-ghm2 · Severity: low — Issue summary: When EVP_PKEY_derive_set_peer() is called with a DHX (X9.42) peer key, the peer...

OS Trackers for CVE-2026-42770

vendor priority summary link
debian unimportant CVE-2026-42770 unimportant priority: Debian including 1 source packages (openssl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-42770
redhat low — https://access.redhat.com/security/cve/CVE-2026-42770
suse medium CVE-2026-42770 severity moderate: SUSE including 52 source package names (compat-openssl098, latest:libexpat1-2.7.1-4.1, …), 356 product×package rows across 70 product lines (Container suse/sl-micro/6.0/baremetal-os-container, Container suse/sl-micro/6.0/base-os-container, … (70 product lines)): Known Not Affected 231, Fixed 69, First Fixed 56. https://www.suse.com/security/cve/CVE-2026-42770/
ubuntu low CVE-2026-42770 low priority: Ubuntu including 5 source packages (edk2, nodejs, openssl, openssl-fips, openssl1.0), 35 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): not-affected 14, DNE 8, needs-triage 8, released 4, needed 1. https://ubuntu.com/security/CVE-2026-42770

Affected software / configurations for CVE-2026-42770

Vendor Product Version Raw CPE
openssl openssl >= 3.0.0, < 3.0.21 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.4.0, < 3.4.6 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.5.0, < 3.5.7 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl >= 3.6.0, < 3.6.3 cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
openssl openssl 4.0.0 cpe:2.3:a:openssl:openssl:4.0.0:-:*:*:*:*:*:*

References for CVE-2026-42770

cvelogic Threat Intelligence