CVE-2026-35199

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{"affected": [{"affectedData": [{"product": "SymCrypt", "vendor": "microsoft", "versions": [{"status": "affected", "version": ">= 103.5.0, < 103.11.0"}]}], "source": "security-advisories@github.com"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:microsoft:symcrypt:*:*:*:*:*:*:*:*", "matchCriteriaId": "850E34D6-8319-4094-8DE2-E9DAE3CD7478", "versionEndExcluding": "103.11.0", "versionStartIncluding": "103.5.0", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "SymCrypt is the core cryptographic function library currently used by Windows. From 103.5.0 to before 103.11.0, The SymCryptXmssSign function passes a 64-bit leaf count value to a helper function that accepts a 32-bit parameter. For XMSS^MT parameter sets with total tree height >= 32 (which includes standard predefined parameters), this causes silent truncation to zero, resulting in a drastically undersized scratch buffer allocation followed by a heap buffer overflow during signature computation. Exploiting this issue would require an application using SymCrypt to perform an XMSS^MT signature using an attacker-controlled parameter set. It is uncommon for applications to allow the use of attacker-controlled parameter sets for signing, since signing is a private key operation, and private keys must be trusted by definition. Additionally, XMSS(^MT) signing should only be performed in a Hardware Security Module (HSM). XMSS(^MT) signing is provided in SymCrypt only for testing purposes. This is a general rule irrespective of this CVE; XMSS(^MT) and other stateful signature schemes are only cryptographically secure when it is guaranteed that the same state cannot be reused for two different signatures, which cannot be guaranteed by software alone. For this reason, XMSS(^MT) signing is also not FIPS approved when performed outside of an HSM. Fixed in version 103.11.0."}, {"lang": "es", "value": "SymCrypt es la biblioteca de funciones criptogr\u00e1ficas central utilizada actualmente por Windows. Desde la versi\u00f3n 103.5.0 hasta antes de la 103.11.0, la funci\u00f3n SymCryptXmssSign pasa un valor de recuento de hojas de 64 bits a una funci\u00f3n auxiliar que acepta un par\u00e1metro de 32 bits. Para conjuntos de par\u00e1metros XMSS^MT con una altura total de \u00e1rbol >= 32 (lo que incluye par\u00e1metros predefinidos est\u00e1ndar), esto causa una truncaci\u00f3n silenciosa a cero, lo que resulta en una asignaci\u00f3n de b\u00fafer temporal dr\u00e1sticamente insuficiente seguida de un desbordamiento de b\u00fafer de pila durante el c\u00e1lculo de la firma. Explotar este problema requerir\u00eda que una aplicaci\u00f3n que use SymCrypt realice una firma XMSS^MT utilizando un conjunto de par\u00e1metros controlado por el atacante. Es poco com\u00fan que las aplicaciones permitan el uso de conjuntos de par\u00e1metros controlados por el atacante para la firma, ya que la firma es una operaci\u00f3n de clave privada, y las claves privadas deben ser confiables por definici\u00f3n. Adem\u00e1s, la firma XMSS(^MT) solo debe realizarse en un M\u00f3dulo de Seguridad de Hardware (HSM). La firma XMSS(^MT) se proporciona en SymCrypt solo con fines de prueba. Esta es una regla general independientemente de este CVE; XMSS(^MT) y otros esquemas de firma con estado solo son criptogr\u00e1ficamente seguros cuando se garantiza que el mismo estado no puede reutilizarse para dos firmas diferentes, lo cual no puede ser garantizado solo por software. Por esta raz\u00f3n, la firma XMSS(^MT) tampoco est\u00e1 aprobada por FIPS cuando se realiza fuera de un HSM. Corregido en la versi\u00f3n 103.11.0."}], "id": "CVE-2026-35199", "lastModified": "2026-07-24T21:10:00.143", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 6.1, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "privilegesRequired": "LOW", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 4.2, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-35199", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-04-07T14:56:16.132141Z", "version": "2.0.3"}}]}, "published": "2026-04-06T20:16:27.543", "references": [{"source": "security-advisories@github.com", "tags": ["Vendor Advisory"], "url": "https://github.com/microsoft/SymCrypt/security/advisories/GHSA-rvj8-8h6x-hjmg"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-122"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[103.5.0,103.11.0)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "cna", "scores": [{"score": 100.0, "source": "cna"}]}, "product": "symcrypt", "vendor": "microsoft"}], "analysis": {"en": {"generated_at": "2026-04-07T01:36:19.579437+00:00", "value": {"mitigation_remediation": ["Upgrade Microsoft SymCrypt to version 103.11.0 or later. ", "If an upgrade is not possible, avoid using SymCryptXmssSign with custom parameter sets and restrict signing to trusted, predefined parameters only. ", "Prefer performing XMSS\u2011MT signing in a Hardware Security Module or other secure enclave rather than in ordinary software. ", "Monitor applications for crashes or memory corruption and apply security updates promptly."], "summary": {"action": "Apply Patch", "impact": "Heap Buffer Overflow"}, "threat_synthesis": {"affected_systems": "Microsoft SymCrypt versions 103.5.0 through 103.10.x are affected. The issue resides in the SymCryptXmssSign facility, which is part of the Windows cryptographic stack. Systems that use SymCrypt directly or via higher\u2011level APIs to perform XMSS\u2011MT signing with custom parameter sets are vulnerable. The vulnerability is fixed in SymCrypt 103.11.0 and later.", "description_and_impact": "SymCrypt, a core cryptographic library built into Windows, contains a heap buffer overflow in the SymCryptXmssSign function. The bug occurs when the routine receives a 64\u2011bit leaf count for an XMSS\u2011MT key and passes it to a helper that expects a 32\u2011bit value. When the leaf count exceeds 32 bits, the helper truncates the value to zero, causing an undersized scratch buffer and a write beyond its bounds during signature computation. The vulnerability is a classic heap overflow (CWE\u2011122) that can corrupt memory and potentially allow an attacker to gain arbitrary code execution or cause a denial of service. The flaw is triggered only when an application performs an XMSS\u2011MT signature with an attacker\u2011controlled parameter set, a scenario that is unlikely in standard Windows deployments because private\u2011key operations normally use trusted parameters and are intended for HSM or testing use.", "risk_and_exploitability": "The CVSS base score is 6.1, indicating moderate severity. EPSS data is unavailable and the vulnerability is not listed in CISA\u2019s Known Exploited Vulnerabilities catalog. Exploitation requires an application that issues a SymCryptXmssSign call with an attacker\u2011controlled XMSS\u2011MT parameter set\u2014a rare scenario because signing is a secret\u2011key operation and XMSS\u2011MT signing is intended for HSM use or testing. As a result, the realistic attack surface is narrow, and practical exploitation would likely be difficult without additional privileges or configuration changes. If the prerequisites can be met, the buffer overflow could lead to arbitrary code execution or denial of service."}}}}, "created": "2026-04-07T06:54:21.879549+00:00", "updated": "2026-04-07T09:37:23.659655+00:00", "vendors": ["microsoft", "microsoft$PRODUCT$symcrypt"]}