wbrawner/openssl
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Fix buffer overrun in RSA signing

Browse source 
The problem occurs in EVP_PKEY_sign() when using RSA with X931 padding.
It is only triggered if the RSA key size is smaller than the digest length.
So with SHA512 you can trigger the overflow with anything less than an RSA
512 bit key. I managed to trigger a 62 byte overflow when using a 16 bit RSA
key. This wasn't sufficient to cause a crash, although your mileage may
vary.

In practice RSA keys of this length are never used and X931 padding is very
rare. Even if someone did use an excessively short RSA key, the chances of
them combining that with a longer digest and X931 padding is very
small. For these reasons I do not believe there is a security implication to
this. Thanks to Kevin Wojtysiak (Int3 Solutions) and Paramjot Oberoi (Int3
Solutions) for reporting this issue.

Reviewed-by: Andy Polyakov <appro@openssl.org>
This commit is contained in:
Matt Caswell 2015-04-29 13:22:18 +01:00
parent 3deeeeb61b
commit 34166d4189
1 changed files with 7 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

8
crypto/rsa/rsa_pmeth.c
View file

@ -195,8 +195,14 @@ static int pkey_rsa_sign(EVP_PKEY_CTX *ctx, unsigned char *sig,
return ret;
ret = sltmp;
} else if (rctx->pad_mode == RSA_X931_PADDING) {
if (!setup_tbuf(rctx, ctx))
if ((size_t)EVP_PKEY_size(ctx->pkey) < tbslen + 1) {
RSAerr(RSA_F_PKEY_RSA_SIGN, RSA_R_KEY_SIZE_TOO_SMALL);
return -1;
}
if (!setup_tbuf(rctx, ctx)) {
RSAerr(RSA_F_PKEY_RSA_SIGN, ERR_R_MALLOC_FAILURE);
return -1;
}
memcpy(rctx->tbuf, tbs, tbslen);
rctx->tbuf[tbslen] = RSA_X931_hash_id(EVP_MD_type(rctx->md));
ret = RSA_private_encrypt(tbslen + 1, rctx->tbuf,