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VulnerabilityPublished

CVE-2026-35199: microsoft SymCrypt · Heap-based Buffer Overflow

Affects microsoft SymCryptSource CVE Database V5

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Not known to be exploited · CVSS 6.1 Medium : upgrade to 103.11.0 when convenient.

Data as of 30 Oct 2026, 06:59 UTC

CVSS 3.1 base score
6.1Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 103.11.0
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 6 Apr 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

What to do

Upgrade SymCrypt and microsoft/SymCrypt to 103.11.0.

Affected software

ProductAffectedFixed in
microsoftSymCryptAffected
  • >=103.5.0 <103.11.0
Fixed in
  • 103.11.0
GitHubmicrosoft/SymCryptpkg:github/microsoft/SymCryptOther threatsAffected
  • >=103.5.0 <103.11.0
Fixed in
  • 103.11.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

This vulnerability is fixed in SymCrypt version 103.11.0. Users should upgrade to version 103.11.0 or later to remediate this issue. Since the vulnerability affects a specific function used primarily for testing and requires attacker-controlled signing parameters, typical usage scenarios are unlikely to be vulnerable. No additional mitigations are indicated.

Description

CVE-2026-35199 is a heap-based buffer overflow vulnerability in Microsoft SymCrypt versions 103.5.0 up to but not including 103.11.0. The issue arises in the SymCryptXmssSign function when a 64-bit leaf count is truncated to 32 bits, causing an undersized buffer allocation and subsequent overflow during signature computation. Exploitation requires an application to perform XMSS^MT signing with attacker-controlled parameters, which is uncommon and generally restricted to trusted private keys or hardware security modules. This vulnerability is fixed in SymCrypt version 103.11.0.

References

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