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CVE-2026-42770 low CVSS 3.7

Vulnerability in Openssl (CVE-2026-42770)

Summary

Vulnerability in Openssl (CVE-2026-42770). Risk of unauthorized operations or information disclosure.

Original description

The description as published by the 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.

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-42770 has been found in Openssl.
Risk of unauthorized operations or information disclosure. CVSS score: 3.7/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Openssl CVE-2026-42770" on the vendor's site.

CVE-2026-42770 (Openssl) — CWE-325 / CVSS v3 3.7
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-325) exists in Openssl.

📍 Affected scope

Check the vendor advisory for the affected versions of Openssl.

🔥 Severity

Severity: Low (CVSS 3.7/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to the patched release per vendor advisory.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Openssl' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'Openssl' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Openssl を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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