From 7dadc2f25990e852f4766a0d3a94bc0b99d02631 Mon Sep 17 00:00:00 2001 From: Janos Follath Date: Fri, 27 Jan 2017 16:05:20 +0000 Subject: [PATCH] ECP: Prevent freeing a buffer on stack The function ecp_mod_koblitz computed the space for the result of a multiplication optimally for that specific case, but unfortunately the function mbedtls_mpi_mul_mpi performs a generic, suboptimal calculation and needs one more limb for the result. Since the result's buffer is on the stack, the best case scenario is that the program stops. This only happened on 64 bit platforms. Fixes #569 --- ChangeLog | 8 ++++++++ library/ecp_curves.c | 6 +++--- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/ChangeLog b/ChangeLog index 51c5e2075..99df526ed 100644 --- a/ChangeLog +++ b/ChangeLog @@ -12,6 +12,14 @@ Security CertificateVerify messages, to prevent SLOTH attacks against TLS 1.2. Introduced by interoperability fix for #513. +Security + * Fixed a bug that caused freeing a buffer that was allocated on the stack, + when verifying the validity of a key on secp224k1. This could be + triggered remotely for example with a maliciously constructed certificate + and might have led to remote code execution on some exotic embedded + platforms. Reported independently by rongsaws and Regina Wilson. + CVE-2017-2784 + Bugfix * Fix output certificate verification flags set by x509_crt_verify_top() when traversing a chain of trusted CA. The issue would cause both flags, diff --git a/library/ecp_curves.c b/library/ecp_curves.c index 9a6e8eb18..a2a5495a9 100644 --- a/library/ecp_curves.c +++ b/library/ecp_curves.c @@ -1213,7 +1213,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t int ret; size_t i; mbedtls_mpi M, R; - mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R]; + mbedtls_mpi_uint Mp[P_KOBLITZ_MAX + P_KOBLITZ_R + 1]; if( N->n < p_limbs ) return( 0 ); @@ -1235,7 +1235,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) ); if( shift != 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) ); - M.n += R.n - adjust; /* Make room for multiplication by R */ + M.n += R.n; /* Make room for multiplication by R */ /* N = A0 */ if( mask != 0 ) @@ -1257,7 +1257,7 @@ static inline int ecp_mod_koblitz( mbedtls_mpi *N, mbedtls_mpi_uint *Rp, size_t memcpy( Mp, N->p + p_limbs - adjust, M.n * sizeof( mbedtls_mpi_uint ) ); if( shift != 0 ) MBEDTLS_MPI_CHK( mbedtls_mpi_shift_r( &M, shift ) ); - M.n += R.n - adjust; /* Make room for multiplication by R */ + M.n += R.n; /* Make room for multiplication by R */ /* N = A0 */ if( mask != 0 )