CVE-2025-65499
📋 TL;DR
An array index error in OISM libcoap's TLS verification callback allows remote attackers to cause denial of service via a crafted DTLS handshake. This affects systems using libcoap with DTLS enabled. The vulnerability triggers when SSL_get_ex_data_X509_STORE_CTX_idx() returns -1, leading to out-of-bounds memory access.
💻 Affected Systems
- OISM libcoap
📦 What is this software?
Libcoap by Libcoap
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker causes service crash or instability through crafted DTLS packets, disrupting CoAP communication.
Likely Case
Denial of service affecting DTLS-enabled CoAP services, potentially disrupting IoT/embedded device communication.
If Mitigated
Limited impact with proper network segmentation and DTLS handshake validation in place.
🎯 Exploit Status
Exploitation requires sending crafted DTLS handshake packets to vulnerable endpoints.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in libcoap 4.3.6 and later
Vendor Advisory: https://github.com/obgm/libcoap/pull/1750
Restart Required: Yes
Instructions:
1. Update libcoap to version 4.3.6 or later. 2. Recompile applications using libcoap. 3. Restart affected services.
🔧 Temporary Workarounds
Disable DTLS
allDisable DTLS support in libcoap configuration if not required.
Recompile libcoap with --disable-dtls configure flag
Network filtering
linuxBlock DTLS handshake packets from untrusted sources.
iptables -A INPUT -p udp --dport 5684 -j DROP (adjust port as needed)
🧯 If You Can't Patch
- Implement network segmentation to isolate CoAP/DTLS traffic
- Deploy intrusion prevention systems to detect anomalous DTLS handshakes
🔍 How to Verify
Check if Vulnerable:
Check libcoap version and verify DTLS is enabled: ldd /path/to/coap-app | grep sslCheck Version:
coap-client --version 2>/dev/null | head -1Verify Fix Applied:
Verify libcoap version is 4.3.6+ and test DTLS handshake functionality.📡 Detection & Monitoring
Log Indicators:
- Unexpected service crashes
- DTLS handshake failures
- SSL/TLS error logs
Network Indicators:
- Multiple DTLS handshake attempts from single source
- Malformed DTLS packets
SIEM Query:
source="coap.log" AND ("crash" OR "segfault" OR "SSL_error")