Commit e97763c9 authored by Dr. Stephen Henson's avatar Dr. Stephen Henson Committed by Matt Caswell
Browse files

Sanity check ticket length. 



If a ticket callback changes the HMAC digest to SHA512 the existing
sanity checks are not sufficient and an attacker could perform a DoS
attack with a malformed ticket. Add additional checks based on
HMAC size.

Thanks to Shi Lei for reporting this bug.

CVE-2016-6302

Reviewed-by: default avatarViktor Dukhovni <viktor@openssl.org>
parent 652c52a6

ssl/t1_lib.c

+7 −3
Original line number Diff line number Diff line
@@ -2969,9 +2969,7 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick, 
    HMAC_CTX *hctx = NULL;

    EVP_CIPHER_CTX *ctx;

    SSL_CTX *tctx = s->initial_ctx;

    /* Need at least keyname + iv + some encrypted data */

    if (eticklen < 48)

        return 2;



    /* Initialize session ticket encryption and HMAC contexts */

    hctx = HMAC_CTX_new();

    if (hctx == NULL)
@@ -3018,6 +3016,12 @@ static int tls_decrypt_ticket(SSL *s, const unsigned char *etick, 
    if (mlen < 0) {

        goto err;

    }

    /* Sanity check ticket length: must exceed keyname + IV + HMAC */

    if (eticklen <=

        TLSEXT_KEYNAME_LENGTH + EVP_CIPHER_CTX_iv_length(ctx) + mlen) {

        ret = 2;

        goto err;

    }

    eticklen -= mlen;

    /* Check HMAC of encrypted ticket */

    if (HMAC_Update(hctx, etick, eticklen) <= 0