From 934ca0714a686673695c055de86064f423984477 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Fri, 6 Jun 2014 14:25:52 -0700 Subject: [PATCH] Fix DTLS handshake message size checks. MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit In |dtls1_reassemble_fragment|, the value of |msg_hdr->frag_off+frag_len| was being checked against the maximum handshake message size, but then |msg_len| bytes were allocated for the fragment buffer. This means that so long as the fragment was within the allowed size, the pending handshake message could consume 16MB + 2MB (for the reassembly bitmap). Approx 10 outstanding handshake messages are allowed, meaning that an attacker could consume ~180MB per DTLS connection. In the non-fragmented path (in |dtls1_process_out_of_seq_message|), no check was applied. Fixes CVE-2014-3506 Wholly based on patch by Adam Langley with one minor amendment. Reviewed-by: Emilia Käsper --- ssl/d1_both.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-) diff --git a/ssl/d1_both.c b/ssl/d1_both.c index 48dcfe2901..b8e6c73a24 100644 --- a/ssl/d1_both.c +++ b/ssl/d1_both.c @@ -587,6 +587,16 @@ dtls1_retrieve_buffered_fragment(SSL *s, long max, int *ok) return 0; } +/* dtls1_max_handshake_message_len returns the maximum number of bytes + * permitted in a DTLS handshake message for |s|. The minimum is 16KB, but may + * be greater if the maximum certificate list size requires it. */ +static unsigned long dtls1_max_handshake_message_len(const SSL *s) + { + unsigned long max_len = DTLS1_HM_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH; + if (max_len < (unsigned long)s->max_cert_list) + return s->max_cert_list; + return max_len; + } static int dtls1_reassemble_fragment(SSL *s, struct hm_header_st* msg_hdr, int *ok) @@ -595,20 +605,10 @@ dtls1_reassemble_fragment(SSL *s, struct hm_header_st* msg_hdr, int *ok) pitem *item = NULL; int i = -1, is_complete; unsigned char seq64be[8]; - unsigned long frag_len = msg_hdr->frag_len, max_len; - - if ((msg_hdr->frag_off+frag_len) > msg_hdr->msg_len) - goto err; - - /* Determine maximum allowed message size. Depends on (user set) - * maximum certificate length, but 16k is minimum. - */ - if (DTLS1_HM_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH < s->max_cert_list) - max_len = s->max_cert_list; - else - max_len = DTLS1_HM_HEADER_LENGTH + SSL3_RT_MAX_ENCRYPTED_LENGTH; + unsigned long frag_len = msg_hdr->frag_len; - if ((msg_hdr->frag_off+frag_len) > max_len) + if ((msg_hdr->frag_off+frag_len) > msg_hdr->msg_len || + msg_hdr->msg_len > dtls1_max_handshake_message_len(s)) goto err; /* Try to find item in queue */ @@ -749,6 +749,9 @@ dtls1_process_out_of_seq_message(SSL *s, struct hm_header_st* msg_hdr, int *ok) if (frag_len && frag_len < msg_hdr->msg_len) return dtls1_reassemble_fragment(s, msg_hdr, ok); + if (frag_len > dtls1_max_handshake_message_len(s)) + goto err; + frag = dtls1_hm_fragment_new(frag_len, 0); if ( frag == NULL) goto err; -- 2.25.1