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crypto/evp: harden RC4_MD5 cipher.

Originally a crash in 32-bit build was reported CHACHA20-POLY1305
cipher. The crash is triggered by truncated packet and is result
of excessive hashing to the edge of accessible memory (or bogus
MAC value is produced if x86 MD5 assembly module is involved). Since
hash operation is read-only it is not considered to be exploitable
beyond a DoS condition.

Thanks to Robert Święcki for report.

CVE-2017-3731

Reviewed-by: Rich Salz <rsalz@openssl.org>
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dot-asm authored and mattcaswell committed Jan 18, 2017
1 parent 8957add commit 51d009043670a627d6abe66894126851cf3690e9
Showing with 2 additions and 0 deletions.
  1. +2 −0 crypto/evp/e_rc4_hmac_md5.c
@@ -269,6 +269,8 @@ static int rc4_hmac_md5_ctrl(EVP_CIPHER_CTX *ctx, int type, int arg,
len = p[arg - 2] << 8 | p[arg - 1];
if (!ctx->encrypt) {
if (len < MD5_DIGEST_LENGTH)
return -1;
len -= MD5_DIGEST_LENGTH;
p[arg - 2] = len >> 8;
p[arg - 1] = len;

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