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OpenSSL Alternative Chains Certificate Forgery MITM Proxy

This module exploits a logic error in OpenSSL by impersonating the server and sending a specially-crafted chain of certificates, resulting in certain checks on untrusted certificates to be bypassed on the client, allowing it to use a valid leaf certificate as a CA certificate to sign a fake certificate. The SSL/TLS session is then proxied to the server allowing the session to continue normally and application data transmitted between the peers to be saved. The valid leaf certificate must not contain the keyUsage extension or it must have at least the keyCertSign bit set (see X509_check_issued function in crypto/x509v3/v3_purp.c); otherwise; X509_verify_cert fails with X509_V_ERR_UNABLE_TO_GET_ISSUER_CERT_LOCALLY. This module requires an active man-in-the-middle attack.

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Module Name



  • David Benjamin
  • Adam Langley
  • Ramon de C Valle <rcvalle [at]>



  • Service



Module Options

To display the available options, load the module within the Metasploit console and run the commands 'show options' or 'show advanced':

msf > use auxiliary/server/openssl_altchainsforgery_mitm_proxy msf auxiliary(openssl_altchainsforgery_mitm_proxy) > show actions ...actions... msf auxiliary(openssl_altchainsforgery_mitm_proxy) > set ACTION <action-name> msf auxiliary(openssl_altchainsforgery_mitm_proxy) > show options and set options... msf auxiliary(openssl_altchainsforgery_mitm_proxy) > run

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