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Tighten CSR extensionRequest bounds

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Don't allow parts of a compound (SEQUENCE or SET) to go beyond the
containing compound.

The inline CSR regression test is derived from the existing "X509 CSR
ASN.1 (OK)" DER test vector. In the extensionRequest attribute, the original
well-formed fragment is:

    a029 3027 06092a864886f70d01090e 311a 3018 ...

where 31 1a is the SET containing the Extensions sequence and 30 18 is the
contained Extensions sequence. The malformed test changes only the SET
length byte, from 1a to 19:

    a029 3027 06092a864886f70d01090e 3119 3018 ...

The attribute SEQUENCE length and the inner Extensions sequence length are
left unchanged. This makes the SET one byte too short for its containing
attribute, so the parser must reject it with
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH instead of parsing the trailing byte as
data outside the SET.

There is no known security impact, just some risk reduction.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2026-05-07 20:29:11 +02:00
parent 6c8ae1ea48
commit cc794d8501
3 changed files with 26 additions and 7 deletions
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3
ChangeLog.d/x509-csr-extension-request-bounds.txt Normal file
View File

@ -0,0 +1,3 @@
Bugfix
* Reject malformed X.509 CSRs where the extensionRequest attribute
wrappers do not exactly contain the requested extensions.

18
library/x509_csr.c
View File

@ -227,18 +227,30 @@ static int x509_csr_parse_attributes(mbedtls_x509_csr *csr,
/* Check that this is an extension-request attribute */
if (MBEDTLS_OID_CMP(MBEDTLS_OID_PKCS9_CSR_EXT_REQ, &attr_oid) == 0) {
if ((ret = mbedtls_asn1_get_tag(p, end, &len,
if ((ret = mbedtls_asn1_get_tag(p, end_attr_data, &len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SET)) != 0) {
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
}
if ((ret = mbedtls_asn1_get_tag(p, end, &len,
const unsigned char *end_set = *p + len;
if (end_set != end_attr_data) {
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
}
if ((ret = mbedtls_asn1_get_tag(p, end_set, &len,
MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE)) !=
0) {
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, ret);
}
if ((ret = x509_csr_parse_extensions(csr, p, *p + len, cb, p_ctx)) != 0) {
const unsigned char *end_exts = *p + len;
if (end_exts != end_set) {
return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS,
MBEDTLS_ERR_ASN1_LENGTH_MISMATCH);
}
if ((ret = x509_csr_parse_extensions(csr, p, end_exts, cb, p_ctx)) != 0) {
return ret;
}

12
tests/suites/test_suite_x509parse.data
View File

@ -2955,6 +2955,10 @@ X509 CSR ASN.1 (OK)
depends_on:PSA_HAVE_ALG_SOME_ECDSA:PSA_WANT_ECC_SECP_R1_256:PSA_WANT_ALG_SHA_1:!MBEDTLS_X509_REMOVE_INFO
mbedtls_x509_csr_parse:"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":"CSR version \: 1\nsubject name \: C=NL, O=PolarSSL, CN=localhost\nsigned using \: ECDSA with SHA1\nEC key size \: 256 bits\n\nkey usage \: Digital Signature, Non Repudiation, Key Encipherment\n":0
X509 CSR ASN.1 (extensionRequest SET length too short)
depends_on:MBEDTLS_PK_CAN_ECDSA_SOME:MBEDTLS_ECP_HAVE_SECP256R1
mbedtls_x509_csr_parse:"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":"":MBEDTLS_ERR_X509_INVALID_EXTENSIONS+MBEDTLS_ERR_ASN1_LENGTH_MISMATCH
X509 CSR ASN.1 (Unsupported critical extension, critical=true)
depends_on:PSA_HAVE_ALG_SOME_ECDSA:PSA_WANT_ECC_SECP_R1_256:PSA_WANT_ALG_SHA_256:!MBEDTLS_X509_REMOVE_INFO
mbedtls_x509_csr_parse:"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":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_UNEXPECTED_TAG)
@ -3090,17 +3094,17 @@ X509 CSR ASN.1 (attributes: invalid len (len > data))
depends_on:PSA_WANT_ALG_SHA_256:PSA_HAVE_ALG_SOME_RSA_VERIFY
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_len1.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_OUT_OF_DATA)
X509 CSR ASN.1 (attributes: invalid len (len < data))
X509 CSR ASN.1 (attributes: extensionRequest SET extends past attribute)
depends_on:PSA_WANT_ALG_SHA_256:PSA_HAVE_ALG_SOME_RSA_VERIFY
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_len2.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_LENGTH_MISMATCH)
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_len2.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_OUT_OF_DATA)
X509 CSR ASN.1 (attributes: extension request invalid len (len > data))
depends_on:PSA_WANT_ALG_SHA_256:PSA_HAVE_ALG_SOME_RSA_VERIFY
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_extension_request_sequence_len1.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_OUT_OF_DATA)
X509 CSR ASN.1 (attributes: extension request invalid len (len < data))
X509 CSR ASN.1 (attributes: extensionRequest sequence shorter than SET)
depends_on:PSA_WANT_ALG_SHA_256:PSA_HAVE_ALG_SOME_RSA_VERIFY
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_extension_request_sequence_len2.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_OUT_OF_DATA)
mbedtls_x509_csr_parse_file:"../framework/data_files/parse_input/test_csr_v3_all_malformed_attributes_extension_request_sequence_len2.csr.der":"":MBEDTLS_ERROR_ADD(MBEDTLS_ERR_X509_INVALID_EXTENSIONS, MBEDTLS_ERR_ASN1_LENGTH_MISMATCH)
X509 CSR ASN.1 (extensions: invalid sequence tag)
depends_on:PSA_WANT_ALG_SHA_256:PSA_HAVE_ALG_SOME_RSA_VERIFY