What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-02 · updated 2026-07-24
• Weakness: CWE-681

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.

Affected products

• smuellerDD leancrypto: before 1.7.1 — fixed in 1.7.1

How to fix

Upgrade to a fixed version: smuellerDD leancrypto 1.7.1. Check the vendor advisory for mitigations.

References

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

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