CVE-2026-26994

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{"affected": [{"affectedData": [{"product": "utls", "vendor": "refraction-networking", "versions": [{"status": "affected", "version": "< 1.7.0"}]}], "source": "security-advisories@github.com"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:refraction-networking:utls:*:*:*:*:*:go:*:*", "matchCriteriaId": "9F530DA4-D661-48AF-9406-4B86A99C9E64", "versionEndExcluding": "1.7.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "uTLS is a fork of crypto/tls, created to customize ClientHello for fingerprinting resistance while still using it for the handshake. In versions 1.6.7 and below, uTLS did not implement the TLS 1.3 downgrade protection mechanism specified in RFC 8446 Section 4.1.3 when using a uTLS ClientHello spec. This allowed an active network adversary to downgrade TLS 1.3 connections initiated by a uTLS client to a lower TLS version (e.g., TLS 1.2) by modifying the ClientHello message to exclude the SupportedVersions extension, causing the server to respond with a TLS 1.2 ServerHello (along with a downgrade canary in the ServerHello random field). Because uTLS did not check the downgrade canary in the ServerHello random field, clients would accept the downgraded connection without detecting the attack. This attack could also be used by an active network attacker to fingerprint uTLS connections. This issue has been fixed in version 1.7.0."}, {"lang": "es", "value": "uTLS es una bifurcaci\u00f3n de crypto/tls, creado para personalizar ClientHello con el fin de resistir la identificaci\u00f3n de huellas digitales mientras se sigue utilizando para el protocolo de enlace. En las versiones 1.6.7 y anteriores, uTLS no implement\u00f3 el mecanismo de protecci\u00f3n contra la degradaci\u00f3n de TLS 1.3 especificado en la Secci\u00f3n 4.1.3 de RFC 8446 cuando se utiliza una especificaci\u00f3n de ClientHello de uTLS. Esto permiti\u00f3 a un adversario de red activo degradar las conexiones TLS 1.3 iniciadas por un cliente de uTLS a una versi\u00f3n de TLS inferior (por ejemplo, TLS 1.2) modificando el mensaje ClientHello para excluir la extensi\u00f3n SupportedVersions, haciendo que el servidor responda con un ServerHello de TLS 1.2 (junto con un 'canary' de degradaci\u00f3n en el campo aleatorio de ServerHello). Debido a que uTLS no verific\u00f3 el 'canary' de degradaci\u00f3n en el campo aleatorio de ServerHello, los clientes aceptar\u00edan la conexi\u00f3n degradada sin detectar el ataque. Este ataque tambi\u00e9n podr\u00eda ser utilizado por un atacante de red activo para la huella digital de conexiones uTLS. Este problema ha sido solucionado en la versi\u00f3n 1.7.0."}], "id": "CVE-2026-26994", "lastModified": "2026-06-17T10:26:30.400", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 2.5, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-26994", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-02-20T15:12:10.465682Z", "version": "2.0.3"}}]}, "published": "2026-02-20T03:16:01.330", "references": [{"source": "security-advisories@github.com", "tags": ["Patch"], "url": "https://github.com/refraction-networking/utls/commit/f8892761e2a4d29054264651d3a86fda83bc83f9"}, {"source": "security-advisories@github.com", "tags": ["Issue Tracking"], "url": "https://github.com/refraction-networking/utls/issues/181"}, {"source": "security-advisories@github.com", "tags": ["Issue Tracking", "Patch"], "url": "https://github.com/refraction-networking/utls/pull/337"}, {"source": "security-advisories@github.com", "tags": ["Patch", "Vendor Advisory"], "url": "https://github.com/refraction-networking/utls/security/advisories/GHSA-pmc3-p9hx-jq96"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-693"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[0,1.7.0)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "cna", "scores": [{"score": 100.0, "source": "cna"}]}, "original": {"product": "utls", "source": "cna", "vendor": "refraction-networking"}, "product": "utls", "vendor": "refraction-networking"}], "analysis": {"en": {"generated_at": "2026-04-17T17:31:31.726276+00:00", "value": {"mitigation_remediation": ["Upgrade uTLS to version 1.7.0 or newer.", "If an upgrade is not immediately possible, disable or replace uTLS usage for sensitive connections and enforce TLS\u202f1.3 with the standard library.", "Monitor for anomalous ClientHello messages and apply network controls to block or alert on potential downgrade attempts."], "summary": {"action": "Patch Immediately", "impact": "TLS 1.3 downgrade without downgrade canary verification"}, "threat_synthesis": {"affected_systems": "The vulnerability affects the refraction\u2011networking uTLS library in versions 1.6.7 and earlier. No other vendors or products are currently listed.", "description_and_impact": "uTLS, a fork of Go\u2019s crypto/tls, does not validate the downgrade canary in the ServerHello random field for TLS 1.3 handshakes. An active attacker can modify the ClientHello to omit the SupportedVersions extension, leading the server to reply with a TLS\u202f1.2 ServerHello that contains a downgrade canary. Because uTLS does not check this canary, the client accepts the downgraded session, allowing a man\u2011in\u2011the\u2011middle to impersonate the server or perform fingerprinting of uTLS traffic. This flaw is a data integrity and authentication weakness identified by CWE\u2011693.", "risk_and_exploitability": "The CVSS score of 6.5 indicates moderate severity, while the EPSS score of less than 1% suggests a low probability of exploitation in the wild. The flaw is not present in the CISA KEV catalog. An attacker would need a position on the network path to alter the ClientHello, so an uncontrolled remote exploit is unlikely, yet the potential to downgrade TLS 1.3 to TLS 1.2 poses a significant risk to confidentiality and integrity for communications that rely on uTLS."}}}}, "created": "2026-02-20T09:52:44.390854+00:00", "updated": "2026-04-17T17:45:24.334824+00:00", "vendors": ["refraction-networking", "refraction-networking$PRODUCT$utls"]}