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More length checks in RSA PKCS1v15 verify

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Tighten ASN.1 parsing of RSA PKCS#1 v1.5 signatures, to avoid a
potential Bleichenbacher-style attack.

Backport to 1.3
This commit is contained in:
Gilles Peskine 2017-05-03 18:32:21 +02:00
parent bb4bebc26a
commit 6de05fa058
2 changed files with 15 additions and 4 deletions
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6
ChangeLog
View File

@ -1,5 +1,11 @@
mbed TLS ChangeLog (Sorted per branch, date)
= mbed TLS 1.3.xx branch released xxxx-xx-xx
Security
* Tighten ASN.1 parsing of RSA PKCS#1 v1.5 signatures, to avoid a
potential Bleichenbacher-style attack.
= mbed TLS 1.3.19 branch released 2017-03-08
Security

13
library/rsa.c
View File

@ -1344,7 +1344,7 @@ int rsa_rsassa_pkcs1_v15_verify( rsa_context *ctx,
{
int ret;
size_t len, siglen, asn1_len;
unsigned char *p, *end;
unsigned char *p, *p0, *end;
unsigned char buf[POLARSSL_MPI_MAX_SIZE];
md_type_t msg_md_alg;
const md_info_t *md_info;
@ -1397,23 +1397,27 @@ int rsa_rsassa_pkcs1_v15_verify( rsa_context *ctx,
// Parse the ASN.1 structure inside the PKCS#1 v1.5 structure
//
p0 = p;
if( ( ret = asn1_get_tag( &p, end, &asn1_len,
ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( asn1_len + 2 != len )
if( p != p0 + 2 || asn1_len + 2 != len )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( ( ret = asn1_get_tag( &p, end, &asn1_len,
ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( asn1_len + 6 + hashlen != len )
if( p != p0 + 4 || asn1_len + 6 + hashlen != len )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( ( ret = asn1_get_tag( &p, end, &oid.len, ASN1_OID ) ) != 0 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( p != p0 + 6 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
oid.p = p;
p += oid.len;
@ -1429,10 +1433,11 @@ int rsa_rsassa_pkcs1_v15_verify( rsa_context *ctx,
if( ( ret = asn1_get_tag( &p, end, &asn1_len, ASN1_NULL ) ) != 0 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
p0 = p;
if( ( ret = asn1_get_tag( &p, end, &asn1_len, ASN1_OCTET_STRING ) ) != 0 )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( asn1_len != hashlen )
if( p != p0 + 2 || asn1_len != hashlen )
return( POLARSSL_ERR_RSA_VERIFY_FAILED );
if( memcmp( p, hash, hashlen ) != 0 )