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Fix: MQTT v5 Property-Packet Protocol Validation and Decode Safety #440

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Merged
embhorn merged 1 commit into from
Nov 7, 2025
Merged

Fix: MQTT v5 Property-Packet Protocol Validation and Decode Safety #440

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32 changes: 24 additions & 8 deletions src/mqtt_packet.c
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Original file line number Diff line number Diff line change
Expand Up @@ -377,13 +377,20 @@ int MqttEncode_Props(MqttPacketType packet, MqttProp* props, byte* buf)

/* TODO: Check against max size. Sometimes all properties are not
expected to be added */
/* TODO: Validate property type is allowed for packet type */

/* loop through the list properties */
while ((cur_prop != NULL) && (rc >= 0))
{
/* TODO: validate packet type */
(void)packet;
if (cur_prop->type >= sizeof(gPropMatrix) / sizeof(gPropMatrix[0])) {
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_PROPERTY);
break;
}

/* Validate property type is allowed for this packet type */
if (!(gPropMatrix[cur_prop->type].packet_type_mask & (1 << packet))) {
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_PROPERTY_MISMATCH);
break;
}

/* Encode the Identifier */
tmp = MqttEncode_Vbi(buf, (word32)cur_prop->type);
Expand Down Expand Up @@ -505,11 +512,12 @@ int MqttDecode_Props(MqttPacketType packet, MqttProp** props, byte* pbuf,
break;
}

/* Decode the Identifier */
if (buf_len < (word32)(buf - pbuf)) {
/* Check boundary before VBI decoding */
if ((buf - pbuf) > (int)buf_len) {
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_OUT_OF_BUFFER);
break;
}
/* Decode the Identifier */
rc = MqttDecode_Vbi(buf, (word32*)&cur_prop->type,
(word32)(buf_len - (buf - pbuf)));
if (rc < 0) {
Expand All @@ -520,14 +528,17 @@ int MqttDecode_Props(MqttPacketType packet, MqttProp** props, byte* pbuf,
total += tmp;
prop_len -= tmp;

/* TODO: Validate property type is allowed for packet type */
(void)packet;

if (cur_prop->type >= sizeof(gPropMatrix) / sizeof(gPropMatrix[0])) {
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_PROPERTY);
break;
}

/* Validate property type is allowed for packet type */
if (!(gPropMatrix[cur_prop->type].packet_type_mask & (1 << packet))) {
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_PROPERTY_MISMATCH);
break;
}

switch (gPropMatrix[cur_prop->type].data)
{
case MQTT_DATA_TYPE_BYTE:
Expand Down Expand Up @@ -561,6 +572,11 @@ int MqttDecode_Props(MqttPacketType packet, MqttProp** props, byte* pbuf,
}
case MQTT_DATA_TYPE_STRING:
{
if ((buf - pbuf) > (int)buf_len) {
/* Should already be caught earlier, but safe to recheck */
rc = MQTT_TRACE_ERROR(MQTT_CODE_ERROR_OUT_OF_BUFFER);
break;
}
tmp = MqttDecode_String(buf,
(const char**)&cur_prop->data_str.str,
&cur_prop->data_str.len,
Expand Down
1 change: 1 addition & 0 deletions wolfmqtt/mqtt_types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -202,6 +202,7 @@ enum MqttPacketResponseCodes {
MQTT_CODE_ERROR_CURL = -16, /* An error in libcurl that is not clearly
* a network, memory, TLS, or system error. */
#endif
MQTT_CODE_ERROR_PROPERTY_MISMATCH = -17,

MQTT_CODE_CONTINUE = -101,
MQTT_CODE_STDIN_WAKE = -102,
Expand Down