h2o picotls Minicrypto Backend ptls_minicrypto_load_private_key stack-based overflow

Summaryinfo

A vulnerability identified as problematic has been detected in h2o picotls. The affected element is the function ptls_minicrypto_load_private_key of the component Minicrypto Backend. The manipulation leads to stack-based overflow. This vulnerability is referenced as CVE-2026-45271. The attack can only be performed from a local environment. No exploit is available.

Detailsinfo

A vulnerability was found in h2o picotls (affected version not known). It has been rated as problematic. This issue affects the function ptls_minicrypto_load_private_key of the component Minicrypto Backend. The manipulation with an unknown input leads to a stack-based overflow vulnerability. Using CWE to declare the problem leads to CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). Impacted is availability. The summary by CVE is:

Picotls is a TLS protocol library that allows users select different crypto backends based on their use case. Picotls implements its own ASN.1 validation helper, which is used by the minicrypto backend while parsing local PKCS#8 private keys. Prior to commit c14231d801407640bc42c2dcf92783409ea6a7c7, the validator recursively descends into constructed ASN.1 elements without enforcing a maximum nesting depth. If an application loads an attacker-supplied private-key file through ptls_minicrypto_load_private_key(), or otherwise calls the public ASN.1 validation API on untrusted DER, a crafted deeply nested ASN.1 structure can exhaust the process stack and crash the application. Note that the libcrypto (OpenSSL) backend does not use the ASN.1 validation helper of picotls, and therefore is immune to this vulnerability. The vulnerability has been addressed in commit c14231d801407640bc42c2dcf92783409ea6a7c7.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-45271 since 05/11/2026. The exploitation is known to be easy. Attacking locally is a requirement. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit.

Applying the patch c14231d801407640bc42c2dcf92783409ea6a7c7 is able to eliminate this problem.

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Productinfo

Vendor

• h2o

Name

• picotls

Website

• Product: https://github.com/h2o/picotls/

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