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Merge pull request #779 from paul-elliott-arm/discrepancy_cert_2_16

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Backport 2.16: Add missing tag check to signature check on certificate load
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Gilles Peskine 2020-12-03 12:19:30 +01:00 committed by GitHub
commit 4c1939738d
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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