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Add tag check to cert algorithm check

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Add missing tag check for algorithm parameters when comparing the
signature in the description part of the cert against the actual
signature whilst loading a certificate. This was found by a
certificate (created by fuzzing) that openssl would not verify, but
mbedtls would.

Regression test added (one of the client certs modified accordingly)

Signed-off-by: Paul Elliott <paul.elliott@arm.com>
This commit is contained in:
Paul Elliott 2020-11-24 17:30:18 +00:00
parent 7bd481cad2
commit 027b601690
5 changed files with 21 additions and 1 deletions
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11
ChangeLog.d/x509-add-tag-check-to-algorithm-params Normal file
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@ -0,0 +1,11 @@
Security
* Fix a compliance issue whereby we were not checking the tag on the
algorithm parameters (only the size) when comparing the signature in the
description part of the cert to the real signature. This meant that a
NULL algorithm parameters entry would look identical to an array of REAL
(size zero) to the library and thus the certificate would be considered
valid. However, if the parameters do not match in *any* way then the
certificate should be considered invalid, and indeed OpenSSL marks these
certs as invalid when mbedtls did not.
Many thanks to guidovranken who found this issue via differential fuzzing
and reported it in #3629.

1
library/x509_crt.c
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@ -1088,6 +1088,7 @@ static int x509_crt_parse_der_core( mbedtls_x509_crt *crt, const unsigned char *
if( crt->sig_oid.len != sig_oid2.len ||
memcmp( crt->sig_oid.p, sig_oid2.p, crt->sig_oid.len ) != 0 ||
sig_params1.tag != sig_params2.tag ||
sig_params1.len != sig_params2.len ||
( sig_params1.len != 0 &&
memcmp( sig_params1.p, sig_params2.p, sig_params1.len ) != 0 ) )

6
tests/data_files/Makefile
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@ -155,7 +155,11 @@ cli-rsa-sha256.crt.der: cli-rsa-sha256.crt
$(OPENSSL) x509 -in $< -out $@ -inform PEM -outform DER
all_final += cli-rsa-sha256.crt.der
cli-rsa.key.der: $(cli_crt_key_file_rsa)
cli-rsa-sha256-badalg.crt.der: cli-rsa-sha256.crt.der
hexdump -ve '1/1 "%.2X"' $< | sed "s/06092A864886F70D01010B0500/06092A864886F70D01010B0900/2" | xxd -r -p > $@
all_final += cli-rsa-sha256-badalg.crt.der
cli-rsa.key.der: $(cli_crt_key_file_rsa)
$(OPENSSL) pkey -in $< -out $@ -inform PEM -outform DER
all_final += cli-rsa.key.der

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tests/data_files/cli-rsa-sha256-badalg.crt.der Normal file
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4
tests/suites/test_suite_x509parse.data
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@ -1876,6 +1876,10 @@ X509 File parse (trailing spaces, OK)
depends_on:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED:MBEDTLS_SHA256_C:MBEDTLS_RSA_C
x509parse_crt_file:"data_files/server7_trailing_space.crt":0
X509 File parse (Algorithm Params Tag mismatch)
depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C
x509parse_crt_file:"data_files/cli-rsa-sha256-badalg.crt.der":MBEDTLS_ERR_X509_SIG_MISMATCH
X509 Get time (UTC no issues)
depends_on:MBEDTLS_X509_USE_C
x509_get_time:MBEDTLS_ASN1_UTC_TIME:"500101000000Z":0:1950:1:1:0:0:0