Vulnerability-Lookup

CVE-2026-35199 (GCVE-0-2026-35199)

Vulnerability from cvelistv5 – Published: 2026-04-06 19:44 – Updated: 2026-04-07 15:10

Title

SymCrypt SymCryptXmssSign function - Heap overflow via 64->32-bit leaf-count truncation

Summary

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.

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-122 - Heap-based Buffer Overflow

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/microsoft/SymCrypt/security/ad…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
microsoft	SymCrypt	Affected: >= 103.5.0, < 103.11.0

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-35199

Vulnerability from fkie_nvd - Published: 2026-04-06 20:16 - Updated: 2026-06-17 10:40

Severity

6.1 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/microsoft/SymCrypt/security/advisories/GHSA-rvj8-8h6x-hjmg	Vendor Advisory

Impacted products

	Vendor	Product	Version
	microsoft	symcrypt	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "SymCrypt",
          "vendor": "microsoft",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 103.5.0, \u003c 103.11.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
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    }
  ],
  "id": "CVE-2026-35199",
  "lastModified": "2026-06-17T10:40:11.850",
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MSRC_CVE-2026-35199

Vulnerability from csaf_microsoft - Published: 2026-04-02 00:00 - Updated: 2026-04-17 01:02

Summary

SymCrypt SymCryptXmssSign function - Heap overflow via 64->32-bit leaf-count truncation

Notes

Additional Resources: To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

Disclaimer: The information provided in the Microsoft Knowledge Base is provided \"as is\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

CVE-2026-35199

6.1 (Medium)


                        
                          CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H

CWE-122 - Heap-based Buffer Overflow

Affected products

Known affected 1 product

Product	Identifier	Version	Remediation
Unresolved product id: 17084-1		—	None Available

References

4 references

URL	Category
https://msrc.microsoft.com/csaf/vex/2026/msrc_cve…	self
https://support.microsoft.com/lifecycle	external
https://www.first.org/cvss	external
https://msrc.microsoft.com/csaf/vex/2026/msrc_cve…	self

JSON

To clipboard

{
  "document": {
    "category": "csaf_vex",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Public",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
      }
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    "lang": "en-US",
    "notes": [
      {
        "category": "general",
        "text": "To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle",
        "title": "Additional Resources"
      },
      {
        "category": "legal_disclaimer",
        "text": "The information provided in the Microsoft Knowledge Base is provided \\\"as is\\\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.",
        "title": "Disclaimer"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "secure@microsoft.com",
      "name": "Microsoft Security Response Center",
      "namespace": "https://msrc.microsoft.com"
    },
    "references": [
      {
        "category": "self",
        "summary": "CVE-2026-35199 SymCrypt SymCryptXmssSign function - Heap overflow via 64-\u003e32-bit leaf-count truncation - VEX",
        "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-35199.json"
      },
      {
        "category": "external",
        "summary": "Microsoft Support Lifecycle",
        "url": "https://support.microsoft.com/lifecycle"
      },
      {
        "category": "external",
        "summary": "Common Vulnerability Scoring System",
        "url": "https://www.first.org/cvss"
      }
    ],
    "title": "SymCrypt SymCryptXmssSign function - Heap overflow via 64-\u003e32-bit leaf-count truncation",
    "tracking": {
      "current_release_date": "2026-04-17T01:02:11.000Z",
      "generator": {
        "date": "2026-04-17T07:18:25.639Z",
        "engine": {
          "name": "MSRC Generator",
          "version": "1.0"
        }
      },
      "id": "msrc_CVE-2026-35199",
      "initial_release_date": "2026-04-02T00:00:00.000Z",
      "revision_history": [
        {
          "date": "2026-04-17T01:02:11.000Z",
          "legacy_version": "1",
          "number": "1",
          "summary": "Information published."
        }
      ],
      "status": "final",
      "version": "1"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "category": "product_version",
                "name": "3.0",
                "product": {
                  "name": "Azure Linux 3.0",
                  "product_id": "17084"
                }
              }
            ],
            "category": "product_name",
            "name": "Azure Linux"
          },
          {
            "branches": [
              {
                "category": "product_version_range",
                "name": "azl3 SymCrypt 103.8.0-1",
                "product": {
                  "name": "azl3 SymCrypt 103.8.0-1",
                  "product_id": "1"
                }
              }
            ],
            "category": "product_name",
            "name": "SymCrypt"
          }
        ],
        "category": "vendor",
        "name": "Microsoft"
      }
    ],
    "relationships": [
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "azl3 SymCrypt 103.8.0-1 as a component of Azure Linux 3.0",
          "product_id": "17084-1"
        },
        "product_reference": "1",
        "relates_to_product_reference": "17084"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-35199",
      "cwe": {
        "id": "CWE-122",
        "name": "Heap-based Buffer Overflow"
      },
      "notes": [
        {
          "category": "general",
          "text": "GitHub_M",
          "title": "Assigning CNA"
        }
      ],
      "product_status": {
        "known_affected": [
          "17084-1"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-35199 SymCrypt SymCryptXmssSign function - Heap overflow via 64-\u003e32-bit leaf-count truncation - VEX",
          "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-35199.json"
        }
      ],
      "remediations": [
        {
          "category": "none_available",
          "date": "2026-04-17T01:02:11.000Z",
          "details": "There is no fix available for this vulnerability as of now",
          "product_ids": [
            "17084-1"
          ]
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "LOCAL",
            "availabilityImpact": "HIGH",
            "baseScore": 6.1,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "environmentalsScore": 0.0,
            "integrityImpact": "LOW",
            "privilegesRequired": "LOW",
            "scope": "UNCHANGED",
            "temporalScore": 6.1,
            "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"
          },
          "products": [
            "17084-1"
          ]
        }
      ],
      "title": "SymCrypt SymCryptXmssSign function - Heap overflow via 64-\u003e32-bit leaf-count truncation"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

CVE-2026-35199 (GCVE-0-2026-35199)

FKIE_CVE-2026-35199

MSRC_CVE-2026-35199

Tags

Sightings

Nomenclature