OpenSSL FFC-DH Peer Validation Uses Attacker-Supplied q
CVE-2026-42770 is an improper finite-field Diffie-Hellman peer-key validation flaw in OpenSSL affecting DHX (X9.42) key agreement through EVP_PKEY_derive_set_peer(). When a DHX peer key is supplied, OpenSSL performs the subgroup membership check Y^q ≡ 1 (mod p) using the q value embedded in the attacker-controlled peer key rather than the local private key's q. Although the peer domain parameters are later compared against the local key's parameters, q is not compared, allowing a malicious peer to provide the victim's p and g, a forged small-prime q value, and a public key Y of corresponding small order that passes validation. This enables a Lim-Lee/small-subgroup-confinement attack in which repeated exchanges leak the victim private key modulo small factors of the cofactor; combining the residues via CRT can recover the full private key. The advisory notes the practical exposure is narrow, primarily CMP deployments with long-lived RA/CA DHX keys and bespoke enterprise or government applications using X9.42 DHX static keys in interactive protocols. OpenSSL FIPS modules in the 4.0, 3.6, 3.5, 3.4, and 3.0 lines are affected.
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Impact
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Exploits
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Affected products & vendors
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Recent activity
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An OpenSSL vulnerability addressed in Alpine Linux 3.24.1 as part of the June 9, 2026 advisory.
A low-severity OpenSSL DHX peer validation flaw where subgroup membership checks use attacker-supplied q, enabling small-subgroup confinement attacks and possible private key recovery in narrow scenarios.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.