CVE ID: CVE-2025-34468
Affected Component: libcoap (Constrained Application Protocol library)
Affected Versions: All versions up to and including 4.3.5, prior to commit 30db3ea
Vulnerability Type: Stack-Based Buffer Overflow
Attack Vector: Remote
Authentication Required: No
User Interaction Required: No
Privilege Required: None
Exploitability: High (under specific configuration)
Exploit Availability: No public exploit at the time of writing (proof-of-concept feasible)
Severity: High
Estimated CVSS v3.1 Score: 8.1 (High)
CVSS Vector (Estimated): AV:N / AC:L / PR:N / UI:N / S:U / C:H / I:H / A:H
Executive Summary
CVE-2025-34468 is a stack-based buffer overflow vulnerability in the address resolution logic of libcoap. The flaw occurs when attacker-controlled hostname data is copied into a fixed-size 256-byte stack buffer without adequate bounds checking.
When libcoap is used with proxy support enabled, a remote attacker can send a specially crafted request containing an excessively long hostname. This can lead to a crash (denial of service) and, under favorable conditions, remote code execution.
This vulnerability is particularly relevant for IoT gateways, CoAP proxies, and embedded systems that expose CoAP proxy functionality to untrusted networks.
Technical Details
Root Cause
The vulnerability stems from improper handling of hostname strings during address resolution in the proxy request handling code path.
Key technical issues:
- A fixed 256-byte stack buffer is used to store hostname data.
- The hostname originates from untrusted, attacker-controlled input.
- No sufficient length validation or truncation is applied before copying.
- A standard unsafe string copy operation allows overflow beyond stack boundaries.
Because the buffer resides on the stack, overflowing it can overwrite:
- Saved frame pointers
- Return addresses
- Adjacent stack variables
Exploitation Conditions
Exploitation requires all of the following:
- The application is linked against a vulnerable version of libcoap
- Proxy functionality is enabled
- The application accepts proxy requests from an attacker-reachable network
- The attacker can supply a crafted hostname in the request
If these conditions are met, exploitation is straightforward.
How an Attacker Could Exploit This
A typical attack flow looks like this:
- The attacker sends a CoAP proxy request to the vulnerable service
- The request includes a maliciously long hostname (significantly larger than 256 bytes)
- libcoap attempts to resolve the hostname
- The hostname is copied into a stack buffer without bounds checking
- The buffer overflows, corrupting stack memory
Possible Outcomes
- Immediate crash of the CoAP service (most common)
- Controlled memory corruption, leading to:
- Instruction pointer overwrite
- Execution of attacker-controlled code (depending on:
- Compiler protections
- Stack canaries
- ASLR
- NX/DEP settings)
Exploitability Assessment
| Condition | Impact |
|---|---|
| Stack canaries disabled | High likelihood of RCE |
| ASLR disabled or weak | Exploitation easier |
| NX disabled | Shellcode execution possible |
| Hardened build | Likely DoS only |
Even in hardened environments, denial of service is trivial.
Proof-of-Concept (PoC) Status
- No public PoC released
- PoC is trivial to develop
- Requires only:
- A CoAP proxy request
- An overlong hostname field (e.g., 1–2 KB)
Security researchers or attackers with protocol knowledge can reproduce this issue easily.
Example Malicious Payload
This is a conceptual illustration, not a weaponized exploit:
coap://proxy-endpoint
Proxy-Uri: coap://AAAAA...(repeated >256 bytes)...AAAA/resource
The excessive hostname length triggers the overflow during resolution.
Detection & Monitoring Guidance
What to Monitor
Focus on proxy-related CoAP traffic.
Log Sources to Enable
- Application logs from the CoAP service
- CoAP proxy request logs
- System crash logs (segfaults)
- Core dump generation (if enabled)
Indicators of Exploitation
- Sudden crashes of the CoAP service
- Repeated segmentation faults
- Abnormally long hostnames in proxy requests
- Unexpected restarts of embedded devices or gateways
Detection Rules
Hostname Length Detection
Alert if:
- Proxy request hostname length exceeds reasonable limits (e.g., >255 characters)
Behavioral Rules
- Multiple proxy requests followed by service crash
- Repeated long hostname attempts from the same source
Mitre ATT&CK Mapping
| Technique ID | Name |
|---|---|
| T1190 | Exploit Public-Facing Application |
| T1068 | Exploitation for Privilege Escalation |
| T1055 | Process Injection (post-exploitation possibility) |
| T1499 | Endpoint Denial of Service |
Business Impact
- Service disruption in IoT and OT environments
- Potential full system compromise of CoAP gateways
- Lateral movement risk in constrained networks
- Loss of integrity and availability in embedded deployments
Remediation & Mitigation
Official Fix (Strongly Recommended)
Upgrade libcoap to a version including commit 30db3ea.
Official Patch Link:
https://github.com/obgm/libcoap/commit/30db3ea
Temporary Mitigations (If Upgrade Is Not Immediately Possible)
- Disable proxy functionality if not strictly required
- Restrict access to CoAP proxy endpoints via:
- Network segmentation
- Firewall rules
- Enforce hostname length validation at the application layer
- Rebuild with:
- Stack canaries enabled
- ASLR enabled
- NX/DEP enabled
Final Takeaway
CVE-2025-34468 is a serious memory corruption vulnerability that affects real-world IoT and embedded deployments using libcoap with proxy support. While exploitation depends on configuration and build options, the ease of triggering a crash and the possibility of remote code execution make this a high-risk issue.
Organizations using libcoap in any proxy-enabled context should prioritize patching immediately.
