CVE-2026-26453 in ccoap
Summary
by MITRE • 08/27/2026
ccoap 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5 contains a null pointer dereference vulnerability in the coap_server_handle_session() function when processing COAP messages containing URI_PATH options with NULL data pointers. When the server searches for a URI_PATH option matching the string "separate", it directly calls strncmp() on option_list[i].data without checking if the pointer is NULL. This causes a segmentation fault when the option's data field is NULL.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified in commit 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5 within the libcoap library represents a critical input validation failure that leads to application instability. The flaw resides specifically in the coap_server_handle_session() function, which is responsible for processing incoming Constrained Application Protocol messages. During normal operation, this function parses various options embedded within COAP packets, including URI_PATH options. In this specific instance, the code attempts to locate a URI_PATH option with the value "separate" by iterating through the list of available options and comparing their data fields against the target string using the strncmp() library function.
The core technical deficiency is the absence of a null pointer check before invoking strncmp(). When processing COAP messages that contain URI_PATH options where the data field is NULL, the application proceeds directly to dereference this invalid memory address. Since strncmp() expects valid pointers for both its arguments and attempts to read from them immediately, passing a NULL pointer results in an immediate segmentation fault. This behavior indicates a fundamental lack of defensive programming practices regarding input integrity checks within the message parsing logic. The vulnerability is triggered by malformed or specifically crafted COAP packets that include URI_PATH options with null data fields, allowing any remote attacker capable of sending such traffic to exploit this flaw.
From an operational perspective, this null pointer dereference results in a denial of service condition for the coap_server process. Upon encountering the invalid memory access, the server application will crash and terminate unexpectedly. This disruption prevents legitimate users from accessing resources hosted on the CoAP server and requires manual intervention or automated restart mechanisms to restore service availability. In environments where high availability is critical, such as IoT gateways or industrial control systems relying on CoAP for communication, this vulnerability can cause significant downtime and operational interruptions. The impact aligns with CWE-476, which describes a NULL Pointer Dereference, highlighting the failure of the software to handle unexpected input values that result in accessing invalid memory locations.
Furthermore, this vulnerability facilitates remote exploitation without authentication if the CoAP server is exposed to untrusted networks. Attackers can craft malicious COAP packets containing URI_PATH options with null data pointers and send them to the vulnerable service endpoint. The resulting crash effectively denies service to all connected clients until the server process is restarted. This scenario reflects common attack patterns found in ATT&CK technique T1498, specifically Network Denial of Service via application layer exploits. It underscores the risk associated with parsing untrusted network data without rigorous validation and sanitization steps prior to processing.
To mitigate this vulnerability, developers must implement strict input validation within the coap_server_handle_session() function. The primary remediation involves adding a conditional check to verify that option_list[i].data is not NULL before passing it to strncmp(). If the pointer is null, the code should either skip the comparison or handle the malformed option gracefully without crashing. Additionally, integrating static analysis tools and fuzzing techniques into the development lifecycle can help identify similar input validation gaps in other parts of the CoAP implementation. Updating to a patched version of libcoap that includes this fix is essential for maintaining system integrity. Organizations should also consider deploying network-level protections such as intrusion detection systems configured to detect anomalous COAP traffic patterns, providing an additional layer of defense against exploitation attempts while patching efforts are underway.