Description
LiamBindle MQTT-C through version 1.1.6 contains a heap-based out-of-bounds read and integer underflow in the mqtt_unpack_publish_response() function in src/mqtt.c that allows a remote unauthenticated attacker controlling an MQTT broker - or able to inject MQTT traffic into an unencrypted session - to crash a subscribed MQTT-C client and potentially disclose adjacent heap memory by sending a single crafted PUBLISH packet. The function validates only that the fixed-header remaining_length is at least 4, then reads the 16-bit topic_name_size field from the broker-controlled packet and advances the parse pointer by that value without verifying that topic_name_size plus the surrounding overhead fits within remaining_length; it subsequently computes application_message_size as remaining_length - topic_name_size - 2 (QoS 0) or - 4 (QoS greater than 0) in unsigned arithmetic, producing an integer underflow that is then passed to memmove(). A PUBLISH packet with topic_name_size = 0xFFFF and remaining_length = 7 advances the parse pointer 65535 bytes past the receive buffer (out-of-bounds read) and causes an application_message_size near 2^32, crashing the process when the resulting memmove() is executed.
A malicious MQTT broker, or a network attacker capable of injecting a single MQTT PUBLISH packet into an unencrypted session that the victim client has subscribed to, sends one crafted packet with topic_name_size = 0xFFFF and remaining_length = 7 to crash an MQTT-C-based client process and optionally disclose adjacent heap bytes through the out-of-bounds read primitive.
Problem types
CWE-191 Integer Underflow (Wrap or Wraparound)
Product status
Any version
Credits
Saidakbarxon Maxsudxonov
References
github.com/LiamBindle/MQTT-C (LiamBindle/MQTT-C - upstream repository (unmaintained since 2022-10-27))
github.com/LiamBindle/MQTT-C/blob/v1.1.6/src/mqtt.c (Vulnerable mqtt_unpack_publish_response() in src/mqtt.c (v1.1.6))
cwe.mitre.org/data/definitions/125.html (CWE-125: Out-of-bounds Read)
cwe.mitre.org/data/definitions/191.html (CWE-191: Integer Underflow (Wrap or Wraparound))