From b8a437ffa09bbf22c04a55015a6d2743cd0b7529 Mon Sep 17 00:00:00 2001 From: Benjamin Kaduk Date: Wed, 19 Jul 2017 17:59:52 -0500 Subject: [PATCH] Fix out-of-bounds read in ctr_XOR Looking at http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-90Ar1.pdf we see that in the CTR_DRBG_Update() algorithm (internal page number 51), the provided input data is (after truncation to seedlen) xor-d with the key and V vector (of length keylen and blocklen respectively). The comment in ctr_XOR notes that xor-ing with 0 is the identity function, so we can just ignore the case when the provided input is shorter than seedlen. The code in ctr_XOR() then proceeds to xor the key with the input, up to the amount of input present, and computes the remaining input that could be used to xor with the V vector, before accessing a full 16-byte stretch of the input vector and ignoring the calculated length. The correct behavior is to respect the supplied input length and only xor the indicated number of bytes. Reviewed-by: Rich Salz (Merged from https://github.com/openssl/openssl/pull/3971) --- crypto/rand/drbg_rand.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/crypto/rand/drbg_rand.c b/crypto/rand/drbg_rand.c index 4ff347c7ea..77d59ec813 100644 --- a/crypto/rand/drbg_rand.c +++ b/crypto/rand/drbg_rand.c @@ -77,7 +77,7 @@ static void ctr_XOR(DRBG_CTR_CTX *cctx, const unsigned char *in, size_t inlen) /* Should never happen */ n = 16; } - for (i = 0; i < 16; i++) + for (i = 0; i < n; i++) cctx->V[i] ^= in[i + cctx->keylen]; } -- 2.34.1