CVE-2026-34580
Published: 07 April 2026
Summary
CVE-2026-34580 is a critical-severity Improper Certificate Validation (CWE-295) vulnerability in Botan Project Botan. Its CVSS base score is 9.3 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 8.7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and RA-5 (Vulnerability Monitoring and Scanning).
Deeper analysis
CVE-2026-34580 affects Botan, a C++ cryptography library, specifically version 3.11.0. The vulnerability stems from the Certificate_Store::certificate_known function, which returns true if any certificate in the store matches the distinguished name (DN) and subject key identifier (SKID), if set, of the provided certificate, without verifying that the certificates are identical. An extension to path validation logic in 3.11.0 incorrectly assumed this function only returned true for identical certificates, leading to flawed validation (CWE-295: Improper Certificate Validation). The CVSS v3.1 base score is 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).
An attacker can exploit this remotely with low complexity and no privileges or user interaction by presenting an end-entity certificate whose DN and SKID match those of a trusted root certificate in the store. The end-entity certificate is then accepted as a trusted root, bypassing proper chain validation. This enables integrity violations, such as impersonating trusted entities in TLS handshakes or other PKI-dependent operations that use Botan for certificate path validation.
The vulnerability is fixed in Botan 3.11.1, as detailed in the project's security advisory at https://github.com/randombit/botan/security/advisories/GHSA-v782-6fq4-q827. Security practitioners using Botan 3.11.0 should upgrade to 3.11.1 or later to mitigate the issue.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-19947
Vulnerability details
Botan is a C++ cryptography library. In 3.11.0, the function Certificate_Store::certificate_known had a misleading name; it would return true if any certificate in the store had a DN (and subject key identifier, if set) matching that of the argument. It…
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did not check that the cert it found and the cert it was passed were actually the same certificate. In 3.11.0 an extension of path validation logic was made which assumed that certificate_known only returned true if the certificates were in fact identical. The impact is that if an end entity certificate is presented, and its DN (and subject key identifier, if set) match that of any trusted root, the end entity certificate is accepted immediately as if it itself were a trusted root. , This vulnerability is fixed in 3.11.1.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The certificate validation bypass allows remote presentation of a forged end-entity certificate accepted as trusted, directly enabling exploitation of public-facing apps for initial access (T1190) and facilitating impersonation of trusted entities in TLS (T1557 Adversary-in-the-Middle).
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely flaw remediation by upgrading Botan from 3.11.0 to 3.11.1 directly fixes the improper certificate validation logic that accepts end-entity certificates as trusted roots.
Establishes and enforces PKI certificate validation requirements including full chain validation and authoritative source checks, mitigating flawed library assumptions about certificate identity matching.
Vulnerability scanning identifies deployments of vulnerable Botan 3.11.0, enabling detection of the improper certificate validation flaw for subsequent remediation.