CVE-2026-26456 in ccoap
Summary
by MITRE • 08/27/2026
A null pointer dereference vulnerability exists in the server-side session management logic of ccoap 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5. The issue is caused by a race condition between the request dispatch thread and the session cleanup thread when accessing shared session list nodes without proper synchronization.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified in ccoap version 77f55c4b466e99327c24ace8a2913d3ba7e2ccd5 represents a critical flaw within the server-side session management architecture, specifically manifesting as a null pointer dereference. This issue stems from an inadequate synchronization mechanism governing access to shared data structures during concurrent operations. In multi-threaded environments such as CoAP servers handling numerous simultaneous requests, maintaining data integrity requires strict locking protocols or atomic operations when modifying shared state. The absence of these safeguards creates a window where the application logic attempts to dereference a memory address that has been invalidated or set to null by another thread, leading to immediate process termination or undefined behavior.
The technical root cause lies in a race condition between two distinct operational threads: the request dispatch thread and the session cleanup thread. The request dispatch thread is responsible for processing incoming CoAP messages and updating associated session states, while the session cleanup thread periodically scans the active session list to remove expired entries based on timeout policies. When these threads operate concurrently without proper mutual exclusion, a scenario arises where the cleanup thread may free or nullify a session node that the dispatch thread is currently attempting to access. Because there are no locks protecting this shared session list during traversal and modification, the dispatch thread can retrieve a pointer to a session object just before it is deallocated by the cleanup thread. Subsequent operations on this now-dangling reference result in a segmentation fault or similar crash due to the null dereference.
From an operational impact perspective, this vulnerability poses a severe risk to service availability and system stability. An attacker can exploit this race condition by generating a high volume of concurrent requests that trigger frequent session creation and expiration cycles. By carefully timing these requests, it is possible to increase the probability of hitting the vulnerable code path during cleanup operations. Successful exploitation leads to denial of service through application crashes or core dumps. In environments where ccoap serves as a gateway for IoT devices, such instability can disrupt critical communications, leading to data loss and operational downtime. Furthermore, while primarily causing availability issues, memory corruption vulnerabilities like null pointer dereferences can sometimes be leveraged in more complex attack chains if the surrounding memory layout allows for controlled overwrites or information disclosure, although the primary vector here is stability degradation.
This flaw aligns with Common Weakness Enumeration CWE-476, which defines a NULL Pointer Dereference as accessing a memory address of zero, typically resulting from improper initialization or failure to check return values before use. Additionally, it relates to CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization, highlighting the lack of proper locking mechanisms in multi-threaded contexts. In terms of attack classification under MITRE ATT&CK, this vulnerability facilitates Denial of Service (T1499) by exhausting system resources or crashing services through crafted concurrent requests that exploit timing dependencies.
To mitigate this vulnerability, developers must implement robust synchronization primitives around the shared session list data structure. This includes using mutex locks to ensure exclusive access during both iteration and modification phases, thereby preventing the cleanup thread from freeing a node while it is being accessed by the dispatch thread. Alternatively, employing reference counting mechanisms can allow safe concurrent reads as long as write operations are serialized or managed through atomic updates. It is also advisable to implement defensive programming practices such as checking for null pointers before dereferencing them and ensuring that session objects remain valid throughout their lifecycle within the request processing context. Regular code audits focusing on concurrency patterns and race conditions in server-side logic will further reduce the likelihood of similar issues arising in future iterations of the software.