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

Quick assessment

Affected
OpenSSL OpenSSL
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

OpenSSL是OpenSSL团队的一个开源的能够实现安全套接层（SSLv2/v3）和安全传输层（TLSv1）协议的通用加密库。该产品支持多种加密算法，包括对称密码、哈希算法、安全散列算法等。 OpenSSL存在安全漏洞，该漏洞源于EVP_PKEY_derive_set_peer处理DHX对等密钥时未正确检查子群成员资格，可能导致私钥恢复。

AI Predicted 5.3 Difficulty: Moderate EPSS 0.26% · P16

Possible ATT&CK Techniques 1 AI

T1552.004 · Private Keys

Affected Version Matrix 5

VendorProduct Version RangeStatus
OpenSSL OpenSSL 4.0.0< 4.0.1 affected
3.6.0< 3.6.3 affected
3.5.0< 3.5.7 affected
3.4.0< 3.4.6 affected
3.0.0< 3.0.21 affected
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I. Basic Information for CVE-2026-42770

Vulnerability Information
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Vulnerability Title
FFC-DH Peer Validation Uses Attacker-Supplied q
Source: CVE Program / CVE List V5
Vulnerability 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, 3.1.2 and 3.0 are affected by this issue.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
缺少必要的密码学步骤
Source: CVE Program / CVE List V5
Vulnerability Title
OpenSSL 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
OpenSSL是OpenSSL团队的一个开源的能够实现安全套接层（SSLv2/v3）和安全传输层（TLSv1）协议的通用加密库。该产品支持多种加密算法，包括对称密码、哈希算法、安全散列算法等。 OpenSSL存在安全漏洞，该漏洞源于EVP_PKEY_derive_set_peer处理DHX对等密钥时未正确检查子群成员资格，可能导致私钥恢复。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
OpenSSL OpenSSL 4.0.0 ~ 4.0.1 -

II. Public POCs for CVE-2026-42770

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III. Intelligence Information for CVE-2026-42770

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Patches & Fixes for CVE-2026-42770 (5)

Vendor Advisories for CVE-2026-42770 (1)

Same Patch Batch · OpenSSL · 2026-06-09 · 18 CVEs total

CVE-2026-45445 AES-OCB IV Ignored on EVP_Cipher() Path
CVE-2026-34183 Unbounded Memory Growth in the QUIC PATH_CHALLENGE Handler
CVE-2026-34181 PKCS#12 Files with PBMAC1 Are Accepted with Short HMAC Keys
CVE-2026-34180 Heap Buffer Over-read in ASN.1 Content Parsing
CVE-2026-34182 CMS AuthEnvelopedData Processing May Accept Forged Messages
CVE-2026-9076 Out-of-Bounds Read in CMS Password-Based Decryption
CVE-2026-35188 Double-free When Checking OCSP Stapled Response
CVE-2026-7383 Possible Heap Buffer Overflow in ASN.1 Multibyte String Conversion
CVE-2026-45446 Incorrect Tag Processing for Empty Messages in AES-GCM-SIV and AES-SIV modes
CVE-2026-42771 Possible Out of Bounds Read in X509_VERIFY_PARAM_set1_email()
CVE-2026-45447 Heap Use-After-Free in the PKCS7_verify() Function
CVE-2026-42768 Multi-RecipientInfo Bleichenbacher Oracle in CMS_decrypt() and PKCS7_decrypt()
CVE-2026-42769 Trust-Anchor Substitution via cert/issuer Typo in CMP rootCaKeyUpdate
CVE-2026-42767 NULL Pointer Dereference in CRMF EncryptedValue Decryption
CVE-2026-42766 Possible NULL Dereference in Password-Based CMS Decryption
CVE-2026-42764 NULL Pointer Dereference in QUIC Server Initial Packet Handling
CVE-2026-42765 NULL Dereference in Certificate Verification with OCSP Checking

IV. Related Vulnerabilities

Same product: OpenSSL
Same vendor: OpenSSL
Same weakness: CWE-325

V. Comments for CVE-2026-42770

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