CVE-2026-34610: leancrypto integer truncation in lc_x509_extract_name_segment

CVE-2026-34610 · Severity: medium · CVSS 5.9 · Published 2026-04-02

leancrypto is a cryptographic library used to provide post-quantum resistant security for digital signatures and certificates. A flaw in how the library processes digital certificates allows an attacker to create a fraudulent certificate that appears to belong to a legitimate user or organization. This could allow an attacker to impersonate a trusted entity, bypass security checks in code signing, or interfere with secure communications.

Quick answers

Is CVE-2026-34610 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-34610 being exploited in the wild.
How severe is CVE-2026-34610?
Medium severity, with a CVSS score of 5.9, published 2 April 2026.
Which products and versions are affected?
smuellerDD leancrypto < 1.7.1.
Is there a fix for CVE-2026-34610?
A patch was published on 2026-03-30: Version 1.7.1 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-34610 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-34610?
Check whether you run Leancrypto. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An integer truncation vulnerability exists in the lc_x509_extract_name_segment() function of the leancrypto library. The function incorrectly casts a size_t value to a uint8_t when storing the length of a Common Name (CN) segment. By crafting a certificate with a CN containing specific padding (e.g., 256 bytes), an attacker can cause the stored length to wrap around, resulting in a parsed CN that matches a victim's identity. This enables identity impersonation during PKCS#7 verification, certificate chain matching, and code signing processes. The vulnerability is addressed in version 1.7.1 by using size_t for length storage and implementing proper bounds checking.

Affected products

  • smuellerDD leancrypto < 1.7.1

Timeline

  • 2026-03-30: patched: Version 1.7.1 released
  • 2026-03-30: advisory: GitHub Security Advisory GHSA-636g-jxv4-v4gr published
  • 2026-04-02: disclosed: CVE-2026-34610 published

References

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