PT-2026-30723 · Microsoft · Symcrypt

Federicoponzi · Published 2026-04-06 · Updated 2026-04-06 · CVE-2026-35199

Positive Technologies (AI Summary)

CVSS v3.1

6.1

Medium

Base vector

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

Name of the Vulnerable Software and Affected Versions SymCrypt versions 103.5.0 through 103.10.999

Description SymCrypt, the core cryptographic function library used by Windows, contains a flaw in the SymCryptXmssSign function. When processing XMSS^MT parameter sets with a total tree height of 32 or greater, a 64-bit leaf count value is truncated to 32 bits when passed to a helper function. This truncation leads to an undersized scratch buffer allocation and a subsequent heap buffer overflow during signature computation. Exploitation requires an application using SymCrypt to perform an XMSS^MT signature with attacker-controlled parameter sets, which is uncommon due to the sensitive nature of signing operations. XMSS(^MT) signing should ideally be performed within a Hardware Security Module (HSM). SymCrypt provides XMSS(^MT) signing primarily for testing purposes. The vulnerability arises from the potential for state reuse in software-based XMSS(^MT) signing, compromising cryptographic security.

Recommendations Update to version 103.11.0 or later.

Fix

Heap Based Buffer Overflow

Weakness Enumeration

CWE-122

Related Identifiers

CVE-2026-35199

Affected Products

Symcrypt

References · 4

• https://github.com/microsoft/SymCrypt/security/advisories/GHSA-rvj8-8h6x-hjmg · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-35199 · Security Note
• https://twitter.com/0dayPublishing/status/2041246954785542234 · Twitter Post
• https://twitter.com/CVEnew/status/2041250712319885719 · Twitter Post