{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/tags/certificate-spoofing/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"cvss":7.1,"id":"CVE-2026-42012"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["GnuTLS"],"_cs_severities":["medium"],"_cs_tags":["vulnerability","certificate spoofing","gnutls","tls"],"_cs_type":"threat","_cs_vendors":["GnuTLS"],"content_html":"\u003cp\u003eCVE-2026-42012 details a certificate validation flaw within the GnuTLS library. This vulnerability arises when GnuTLS processes certificates containing Uniform Resource Identifier (URI) or Service (SRV) Subject Alternative Names (SANs). An attacker can exploit this flaw by crafting a malicious certificate that, when presented to a GnuTLS-enabled application, causes the certificate validation process to incorrectly fall back to checking DNS hostnames against the certificate\u0026rsquo;s Common Name (CN). This fallback mechanism bypasses the intended security checks provided by SANs, allowing the attacker to potentially spoof legitimate services or intercept sensitive information transmitted over TLS/SSL connections. This can affect any application that relies on GnuTLS for secure communication.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker crafts a malicious X.509 certificate. This certificate includes URI or SRV Subject Alternative Names (SANs) designed to trigger the fallback.\u003c/li\u003e\n\u003cli\u003eThe malicious certificate is presented to a GnuTLS-enabled client or server during a TLS/SSL handshake.\u003c/li\u003e\n\u003cli\u003eGnuTLS attempts to validate the certificate. Due to the presence of the specific SAN types, the validation process enters a flawed code path.\u003c/li\u003e\n\u003cli\u003eThe flawed validation process incorrectly falls back to comparing the DNS hostname against the certificate\u0026rsquo;s Common Name (CN).\u003c/li\u003e\n\u003cli\u003eThe attacker ensures the CN matches the targeted service\u0026rsquo;s hostname, bypassing the intended SAN validation.\u003c/li\u003e\n\u003cli\u003eThe GnuTLS library incorrectly marks the certificate as valid.\u003c/li\u003e\n\u003cli\u003eThe TLS/SSL connection is established using the spoofed certificate.\u003c/li\u003e\n\u003cli\u003eThe attacker can then intercept or spoof the legitimate service, potentially gaining access to sensitive information or performing unauthorized actions.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of CVE-2026-42012 can lead to man-in-the-middle attacks, allowing attackers to intercept sensitive data transmitted over TLS/SSL connections. This can include credentials, financial information, and other confidential data. The vulnerability affects any application or service that uses GnuTLS for certificate validation, potentially impacting a wide range of systems. The CVSS v3.1 base score is 7.1, indicating a high potential for exploitation and significant impact on confidentiality and integrity.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade to the latest version of GnuTLS as soon as a patch is available from the vendor to remediate CVE-2026-42012.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u0026ldquo;Detect GnuTLS Certificate Validation Fallback\u0026rdquo; to identify potential exploitation attempts by monitoring for TLS connections with certificates using URI or SRV SANs that trigger the fallback mechanism.\u003c/li\u003e\n\u003cli\u003eEnable verbose logging in GnuTLS to capture detailed information about certificate validation processes. This will aid in investigating potential exploitation attempts (see logsource).\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-05-26T22:18:37Z","date_published":"2026-05-26T22:18:37Z","id":"https://feed.craftedsignal.io/briefs/2026-05-gnutls-certificate-spoofing/","summary":"CVE-2026-42012 describes a vulnerability in GnuTLS where a remote attacker can spoof legitimate services or intercept sensitive information by presenting a specially crafted certificate with URI or SRV SANs, causing the certificate validation process to incorrectly fall back to checking DNS hostnames against the Common Name (CN).","title":"GnuTLS Certificate Spoofing Vulnerability (CVE-2026-42012)","url":"https://feed.craftedsignal.io/briefs/2026-05-gnutls-certificate-spoofing/"}],"language":"en","title":"CraftedSignal Threat Feed — Certificate Spoofing","version":"https://jsonfeed.org/version/1.1"}