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8c5896a74d
No obvious hot-cases. Maybe the describe_file() ones or the intel ones if/when there are hot intel hits.
212 lines
7.3 KiB
Text
212 lines
7.3 KiB
Text
##! Perform validation of Signed Certificate Timestamps, as used
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##! for Certificate Transparency. See RFC6962 for more details.
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@load base/protocols/ssl
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@load protocols/ssl/validate-certs
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# We need to know issuer certificates to be able to determine the IssuerKeyHash,
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# which is required for validating certificate extensions.
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redef SSL::ssl_store_valid_chain = T;
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module SSL;
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export {
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## List of the different sources for Signed Certificate Timestamp
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type SctSource: enum {
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## Signed Certificate Timestamp was encountered in the extension of
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## an X.509 certificate.
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SCT_X509_EXT,
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## Signed Certificate Timestamp was encountered in an TLS session
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## extension.
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SCT_TLS_EXT,
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## Signed Certificate Timestamp was encountered in the extension of
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## an stapled OCSP reply.
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SCT_OCSP_EXT
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};
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## This record is used to store information about the SCTs that are
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## encountered in a SSL connection.
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type SctInfo: record {
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## The version of the encountered SCT (should always be 0 for v1).
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version: count;
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## The ID of the log issuing this SCT.
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logid: string;
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## The timestamp at which this SCT was issued measured since the
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## epoch (January 1, 1970, 00:00), ignoring leap seconds, in
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## milliseconds. Not converted to a Zeek timestamp because we need
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## the exact value for validation.
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timestamp: count;
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## The signature algorithm used for this sct.
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sig_alg: count;
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## The hash algorithm used for this sct.
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hash_alg: count;
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## The signature of this SCT.
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signature: string;
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## Source of this SCT.
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source: SctSource;
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## Validation result of this SCT.
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valid: bool &optional;
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};
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redef record Info += {
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## Number of valid SCTs that were encountered in the connection.
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valid_scts: count &optional;
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## Number of SCTs that could not be validated that were encountered in the connection.
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invalid_scts: count &optional;
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## Number of different Logs for which valid SCTs were encountered in the connection.
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valid_ct_logs: count &log &optional;
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## Number of different Log operators of which valid SCTs were encountered in the connection.
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valid_ct_operators: count &log &optional;
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## List of operators for which valid SCTs were encountered in the connection.
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valid_ct_operators_list: set[string] &optional;
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## Information about all SCTs that were encountered in the connection.
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ct_proofs: vector of SctInfo &default=vector();
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};
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}
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# Used to cache validations for 5 minutes to lessen computational load.
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global recently_validated_scts: table[string] of bool = table()
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&read_expire=5mins &redef;
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event zeek_init()
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{
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Files::register_for_mime_type(Files::ANALYZER_OCSP_REPLY, "application/ocsp-response");
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}
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event ssl_extension_signed_certificate_timestamp(c: connection, is_client: bool, version: count, logid: string, timestamp: count, signature_and_hashalgorithm: SSL::SignatureAndHashAlgorithm, signature: string) &priority=5
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{
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c$ssl$ct_proofs += SctInfo($version=version, $logid=logid, $timestamp=timestamp, $sig_alg=signature_and_hashalgorithm$SignatureAlgorithm, $hash_alg=signature_and_hashalgorithm$HashAlgorithm, $signature=signature, $source=SCT_TLS_EXT);
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}
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event x509_ocsp_ext_signed_certificate_timestamp(f: fa_file, version: count, logid: string, timestamp: count, hash_algorithm: count, signature_algorithm: count, signature: string) &priority=5
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{
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local src: SctSource;
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if ( ! f?$info )
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return;
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if ( f$source == "SSL" && f$info$mime_type == "application/ocsp-response" )
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src = SCT_OCSP_EXT;
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else if ( f$source == "SSL" && f$info$mime_type == "application/x-x509-user-cert" )
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src = SCT_X509_EXT;
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else
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return;
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if ( |f$conns| != 1 )
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return;
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local c: connection &is_assigned;
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for ( _, c in f$conns )
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{
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if ( ! c?$ssl )
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return;
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}
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c$ssl$ct_proofs += SctInfo($version=version, $logid=logid, $timestamp=timestamp, $sig_alg=signature_algorithm, $hash_alg=hash_algorithm, $signature=signature, $source=src);
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}
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# Priority = 19 will be handled after validation is done
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hook ssl_finishing(c: connection) &priority=19
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{
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if ( ! c$ssl?$cert_chain || |c$ssl$cert_chain| == 0 || ! c$ssl$cert_chain[0]?$x509 )
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return;
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local cert = c$ssl$cert_chain[0]$x509$handle;
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local certhash = c$ssl$cert_chain[0]$sha1;
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local issuer_name_hash = x509_issuer_name_hash(cert, 4);
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local valid_proofs = 0;
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local invalid_proofs = 0;
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c$ssl$valid_ct_operators_list = string_set();
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local valid_logs = string_set();
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local issuer_key_hash = "";
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for ( i in c$ssl$ct_proofs )
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{
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local proof = c$ssl$ct_proofs[i];
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if ( proof$logid !in SSL::ct_logs )
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{
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# Well, if we don't know the log, there is nothing to do here...
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proof$valid = F;
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next;
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}
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local log = SSL::ct_logs[proof$logid];
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local valid = F;
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local found_cache = F;
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local validatestring = cat(certhash,proof$logid,proof$timestamp,proof$hash_alg,proof$signature,proof$source);
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if ( proof$source == SCT_X509_EXT && c$ssl?$validation_code )
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validatestring = cat(validatestring, c$ssl$validation_code);
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local validate_hash = sha1_hash(validatestring);
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if ( validate_hash in recently_validated_scts )
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{
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valid = recently_validated_scts[validate_hash];
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found_cache = T;
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}
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if ( found_cache == F && ( proof$source == SCT_TLS_EXT || proof$source == SCT_OCSP_EXT ) )
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{
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valid = sct_verify(cert, proof$logid, log$key, proof$signature, proof$timestamp, proof$hash_alg);
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}
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else if ( found_cache == F )
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{
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# X.509 proof. Here things get awkward because we need information about
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# the issuer cert... and we need to try a few times, because we have to see if we got
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# the right issuer cert.
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#
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# First - Let's try if a previous round already established the correct issuer key hash.
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if ( issuer_key_hash != "" )
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{
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valid = sct_verify(cert, proof$logid, log$key, proof$signature, proof$timestamp, proof$hash_alg, issuer_key_hash);
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}
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# Second - let's see if we might already know the issuer cert through verification.
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if ( ! valid && issuer_name_hash in intermediate_cache )
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{
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issuer_key_hash = x509_spki_hash(intermediate_cache[issuer_name_hash][0], 4);
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valid = sct_verify(cert, proof$logid, log$key, proof$signature, proof$timestamp, proof$hash_alg, issuer_key_hash);
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}
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if ( ! valid && c$ssl?$valid_chain && |c$ssl$valid_chain| >= 2 )
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{
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issuer_key_hash = x509_spki_hash(c$ssl$valid_chain[1], 4);
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valid = sct_verify(cert, proof$logid, log$key, proof$signature, proof$timestamp, proof$hash_alg, issuer_key_hash);
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}
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# ok, if it still did not work - let's just try with all the certs that were sent
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# in the connection. Perhaps it will work with one of them.
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if ( !valid )
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for ( i in c$ssl$cert_chain )
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{
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if ( i == 0 ) # end-host-cert
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next;
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if ( ! c$ssl$cert_chain[i]?$x509 || ! c$ssl$cert_chain[i]$x509?$handle )
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next;
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issuer_key_hash = x509_spki_hash(c$ssl$cert_chain[i]$x509$handle, 4);
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valid = sct_verify(cert, proof$logid, log$key, proof$signature, proof$timestamp, proof$hash_alg, issuer_key_hash);
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if ( valid )
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break;
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}
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}
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if ( ! found_cache )
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recently_validated_scts[validate_hash] = valid;
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proof$valid = valid;
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if ( valid )
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{
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++valid_proofs;
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add c$ssl$valid_ct_operators_list[log$operator];
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add valid_logs[proof$logid];
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}
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else
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++invalid_proofs;
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}
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c$ssl$valid_scts = valid_proofs;
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c$ssl$invalid_scts = invalid_proofs;
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c$ssl$valid_ct_operators = |c$ssl$valid_ct_operators_list|;
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c$ssl$valid_ct_logs = |valid_logs|;
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}
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