CVE-2017-13052 (Other, published 2017-09-14T06:29Z)
Description: value: The CFM parser in tcpdump before 4.9.2 has a buffer over-read in print-cfm.c:cfm_print().
Severity: HIGH (CVSS v3 base score: 9.8)
Weakness: CWE-125 \u2014 Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
Repository: https://github.com/the-tcpdump-group/tcpdump
Files changed:
print-cfm.c
tests/TESTLIST
tests/cfm_sender_id-oobr.out
Commit message: CVE-2017-13052/CFM: refine decoding of the Sender ID TLV

In cfm_network_addr_print() add a length argument and use it to validate
the input buffer.

In cfm_print() add a length check for MAC address chassis ID. Supply
cfm_network_addr_print() with the length of its buffer and a correct
pointer to the buffer (it was off-by-one before). Change some error
handling blocks to skip to the next TLV in the current PDU rather than to
stop decoding the PDU. Print the management domain and address contents,
although in hex only so far.

Add some comments to clarify the code flow and to tell exact sections in
IEEE standard documents. Add new error messages and make some existing
messages more specific.

This fixes a buffer over-read discovered by Bhargava Shastry,
SecT/TU Berlin.

Add a test using the capture file supplied by the reporter(s).


Vulnerable code:
                       register const u_char *tptr)
                return;
                    return;
                    return;
                    hexdump |= cfm_network_addr_print(ndo, tptr);
                return;
                    return;
                    ND_PRINT((ndo, "\n\t  (TLV too short)"));
                    return;

Fixed code:
                       register const u_char *tptr, const u_int length)
    if (length < 1) {
        ND_PRINT((ndo, "\n\t  Network Address Type (invalid, no data"));
        return hexdump;
    }
    /* The calling function must make any due ND_TCHECK calls. */
        if (length != 1 + 4) {
            ND_PRINT((ndo, "(invalid IPv4 address length %u)", length - 1));
            hexdump = TRUE;
            break;
        }
        if (length != 1 + 16) {
            ND_PRINT((ndo, "(invalid IPv6 address length %u)", length - 1));
            hexdump = TRUE;
            break;
        }
                goto next_tlv;
             * IEEE 802.1Q-2014 Section 21.5.3.1
                /*
                 * IEEE 802.1Q-2014 Section 21.5.3.2: Chassis ID Subtype, references
                 * IEEE 802.1AB-2005 Section 9.5.2.2, subsequently
                 * IEEE 802.1AB-2016 Section 8.5.2.2: chassis ID subtype
                 */
                    goto next_tlv;
                    goto next_tlv;
                /* IEEE 802.1Q-2014 Section 21.5.3.3: Chassis ID */
                    if (chassis_id_length != ETHER_ADDR_LEN) {
                        ND_PRINT((ndo, " (invalid MAC address length)"));
                        hexdump = TRUE;
                        break;
                    }
                    hexdump |= cfm_network_addr_print(ndo, tptr + 1, chassis_id_length);
             * IEEE 802.1Q-2014 Section 21.5.3.4: Management Address Domain Length
             * This and all subsequent fields are not present if the TLV length
             * allows only the above fields.
                break;
            /* Here mgmt_addr_length stands for the management domain length. */
            ND_PRINT((ndo, "\n\t  Management Address Domain Length %u", mgmt_addr_length));
                /* IEEE 802.1Q-2014 Section 21.5.3.5: Management Address Domain */
                    goto next_tlv;
                hex_print(ndo, "\n\t  Management Address Domain: ", tptr, mgmt_addr_length);
                /*
                 * IEEE 802.1Q-2014 Section 21.5.3.6: Management Address Length
                 * This field is present if Management Address Domain Length is not 0.
                 */
                    ND_PRINT((ndo, " (Management Address Length is missing)"));
                    hexdump = TRUE;
                    break;
                /* Here mgmt_addr_length stands for the management address length. */
                ND_PRINT((ndo, "\n\t  Management Address Length %u", mgmt_addr_length));
                    /* IEEE 802.1Q-2014 Section 21.5.3.7: Management Address */
                    hex_print(ndo, "\n\t  Management Address: ", tptr, mgmt_addr_length);
next_tlv:
cfm_sender_id-oobr	cfm_sender_id-oobr.pcap	cfm_sender_id-oobr.out	-v -c1
CFMv0 unknown (255), MD Level 0, length 65556
	First TLV offset 0
	  0x0000:  ff00 0001 0004 0104 9a00 000c fb
	Unknown TLV (0xff), length 0
	Sender ID TLV (0x01), length 4
	  Chassis-ID Type MAC address (4), Chassis-ID length 1 (invalid MAC address length)
	  Management Address Domain Length 0
	End TLV (0x00)