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How the CVE Works:
The vulnerability exists within the `coap_dtls_generate_cookie()` function in the libcoap library’s OpenSSL integration code. During a DTLS handshake, the function calls `SSL_get_SSL_CTX()` to retrieve the SSL context pointer from a DTLS session object. A remotely initiated, crafted DTLS handshake packet can be constructed such that this function returns a NULL pointer. The libcoap code subsequently dereferences this NULL pointer without performing a proper validation check. This NULL pointer dereference leads to an immediate segmentation fault and crash of the application using the library, resulting in a reliable denial-of-service condition against the CoAP DTLS server.
DailyCVE Form:
Platform: OISM libcoap
Version: 4.3.5
Vulnerability: NULL pointer dereference
Severity: Critical
Date: 11/24/2025
Prediction: Q1 2026 patch
What Undercode Say:
Analytics:
Find potentially vulnerable systems using libcoap find /usr -name "libcoap" 2>/dev/null ldd /path/to/coap_app | grep -i coap Simulate DTLS traffic to a CoAP port openssl s_client -dtls -connect <target>:5684
// Code snippet highlighting the vulnerable pattern in coap_openssl.c // In function: coap_dtls_generate_cookie() SSL_CTX ctx = SSL_get_SSL_CTX(ssl); // May return NULL // Missing NULL check before dereference unsigned char cookie = SSL_CTX_get_app_data(ctx); // CRASH
How Exploit:
Attacker sends crafted DTLS ClientHello packet to CoAP server port (e.g., 5684). The malicious packet triggers the internal SSL context to be NULL. Libcoap dereferences NULL, causing segmentation fault. Server process crashes, denying service.
Protection from this CVE:
Apply vendor patch. Implement input validation. Use NULL pointer checks.
Impact:
Reliable denial-of-service. Service disruption.
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Sources:
Reported By: nvd.nist.gov
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