From 34166d41892643a36ad2d1f53cc0025e2edc2a39 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Wed, 29 Apr 2015 13:22:18 +0100 Subject: [PATCH] Fix buffer overrun in RSA signing 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 --- crypto/rsa/rsa_pmeth.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/crypto/rsa/rsa_pmeth.c b/crypto/rsa/rsa_pmeth.c index 0aaca9ee14..91dc668ce7 100644 --- a/crypto/rsa/rsa_pmeth.c +++ b/crypto/rsa/rsa_pmeth.c @@ -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, -- 2.25.1