CVE-2026-35199: microsoft SymCrypt · Heap-based Buffer Overflow
Affects microsoft SymCryptSource CVE Database V5
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 6 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| microsoftSymCrypt | Affected
| Fixed in
|
GitHubmicrosoft/SymCryptpkg:github/microsoft/SymCryptOther threats | Affected
| Fixed in
|
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.