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Vulnerabilities

Vulnerability · CVE-2026-35199

SymCrypt is the core cryptographic function library currently used by Windows.

Published Apr 6, 2026 · catalog updated Jul 24, 2026 · SymCrypt is the core

Check if you run it

No confirmed exploitation is on record for CVE-2026-35199. EPSS is 0.35%. Act only if a listed version of SymCrypt is the core is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (SymCrypt is the core).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.1
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.35%
Remediation
Advisory link
Affected products
cpe microsoft/symcrypt

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

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  • cpe microsoft/symcryptversion unspecified

How to fix CVE-2026-35199

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-35199. EPSS is 0.35%. Act only if a listed version of SymCrypt is the core is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-122: Heap-based Buffer Overflow. EPSS 0.35%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Windows security

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 6, 2026 · NIST NVD

    Detected

    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

  2. Jul 24, 2026 · NIST NVD

    Updated

    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

Sources

  • CVE.orgVulnerability recordCVE-2026-35199

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-35199

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-2026-35199

    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 >

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.