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The vulnerability is a NULL pointer dereference in the coap_dtls_generate_cookie() function within src/coap_openssl.c of OISM libcoap version 4.3.5. This function handles DTLS handshake cookies for DoS protection. During a crafted DTLS handshake, the function calls SSL_get_SSL_CTX() to retrieve the SSL context pointer. In malicious cases, this call returns NULL due to improper handshake crafting. The code fails to validate this pointer before dereferencing it, leading to a NULL pointer dereference. This causes the application to crash, resulting in denial of service. Attackers remotely trigger this by sending malicious DTLS packets, disrupting service availability without authentication. The issue stems from missing checks on SSL context validity, assuming non-NULL returns.
Platform: OISM libcoap
Version: 4.3.5
Vulnerability: NULL pointer dereference
Severity: Critical
date: 11/24/2025
Prediction: Patch Q1 2026
What Undercode Say:
Analytics:
grep -r “coap_dtls_generate_cookie” .
strings libcoap.so | grep “SSL_get_SSL_CTX”
test -f src/coap_openssl.c && echo “Vulnerable file present”
how Exploit:
Send crafted DTLS handshake to trigger NULL dereference, causing crash.
Protection from this CVE:
Update to patched version, validate SSL context pointers, use input sanitization.
Impact:
Remote denial of service, application crash, service disruption.
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Sources:
Reported By: nvd.nist.gov
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