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The CVE-2025-65497 vulnerability involves a NULL pointer dereference in the coap_dtls_generate_cookie() function within the src/coap_openssl.c file of OISM libcoap version 4.3.5. This function is part of the DTLS (Datagram Transport Layer Security) implementation used for securing CoAP (Constrained Application Protocol) communications. During a DTLS handshake, the function calls SSL_get_SSL_CTX() to retrieve the SSL context pointer associated with a given SSL session. However, when a remote attacker crafts a malicious DTLS handshake message, it can trigger SSL_get_SSL_CTX() to return a NULL pointer instead of a valid context. The code in coap_dtls_generate_cookie() then attempts to dereference this NULL pointer, leading to a segmentation fault or crash in the application. This dereference occurs because the function does not properly check the return value of SSL_get_SSL_CTX() for NULL before using it. As a result, the libcoap library or any application using it may abruptly terminate, causing a denial of service (DoS). The vulnerability is exploitable remotely without authentication, as the attacker only needs to send a crafted DTLS packet to the affected service. This issue stems from inadequate error handling in the OpenSSL integration code, assuming that SSL_get_SSL_CTX() always returns a valid pointer. The crash can disrupt CoAP-based IoT devices or servers, rendering them unavailable. Fixing this requires adding a NULL check before dereferencing the pointer in the coap_dtls_generate_cookie() function.
Platform: OISM libcoap
Version: 4.3.5
Vulnerability: NULL pointer dereference
Severity: Medium
date: 11/24/2025
Prediction: Patch TBA
What Undercode Say:
Analytics:
Check libcoap version coap-client --version Compile with debug symbols gcc -g -o coap_test coap_source.c -lcoap Use gdb to analyze crash gdb ./coap_test Network capture for DTLS tcpdump -i any -w dtls.pcap port 5684
// Code snippet from coap_openssl.c
SSL_CTX ctx = SSL_get_SSL_CTX(ssl);
if (!ctx) {
// Missing NULL check leads to dereference
return error;
}
// Vulnerable dereference
char cookie = ctx->generate_cookie(data);
how Exploit:
Craft malicious DTLS handshake packets targeting coap_dtls_generate_cookie() to trigger NULL return from SSL_get_SSL_CTX(), causing crash and DoS.
Protection from this CVE:
Update libcoap to patched version, implement input validation, use firewall rules to limit DTLS traffic, and monitor for crashes.
Impact:
Denial of service, application crash, disruption of IoT communications.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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