CVE-2025-29329: Sagemcom F@st 3686 RCE Vulnerability

CVE-2025-29329 Overview

A buffer overflow vulnerability exists in the ippprint (Internet Printing Protocol) service on Sagemcom F@st 3686 routers running firmware version MAGYAR_4.121.0. This vulnerability allows remote attackers to execute arbitrary code on affected devices by sending a specially crafted HTTP request to the IPP printing service.

Critical Impact

Remote attackers can achieve arbitrary code execution on vulnerable Sagemcom routers without authentication, potentially leading to complete device compromise, network pivoting, and persistent access to the local network.

Affected Products

• Sagemcom F@st 3686 with firmware version MAGYAR_4.121.0
• Devices with the ippprint (Internet Printing Protocol) service enabled

Discovery Timeline

• 2026-01-12 - CVE-2025-29329 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-29329

Vulnerability Analysis

This vulnerability is classified as CWE-120 (Buffer Copy without Checking Size of Input), a classic buffer overflow condition. The ippprint service, which implements the Internet Printing Protocol on Sagemcom F@st 3686 routers, fails to properly validate the size of input data received via HTTP requests before copying it into a fixed-size buffer.

When the ippprint service processes incoming HTTP requests, it allocates a buffer of predetermined size to handle request data. However, the service does not enforce proper bounds checking, allowing an attacker to submit request data that exceeds the allocated buffer space. This overflow condition can overwrite adjacent memory regions, including return addresses and function pointers, enabling the attacker to redirect program execution to attacker-controlled code.

The network-accessible nature of this vulnerability is particularly concerning for residential router deployments. The attack requires no authentication and can be executed remotely by any attacker who can reach the vulnerable service, either from the local network or potentially from the internet if the service is exposed.

Root Cause

The root cause of this vulnerability lies in the ippprint service's failure to implement proper input validation and boundary checks when processing HTTP request data. The service uses unsafe memory copy operations that do not verify the length of incoming data against the destination buffer size, resulting in a classic stack-based or heap-based buffer overflow condition.

Attack Vector

This vulnerability is exploitable over the network via HTTP requests sent to the ippprint service. An attacker crafts a malicious HTTP request containing an oversized payload targeting specific input fields processed by the vulnerable service. When the ippprint service attempts to process this request, the overflow occurs, allowing the attacker to:

1. Overwrite critical memory structures on the stack or heap
2. Corrupt return addresses or function pointers
3. Redirect execution flow to shellcode embedded in the malicious request
4. Achieve arbitrary code execution with the privileges of the ippprint service

The attack requires no user interaction and no prior authentication, making it highly exploitable in real-world scenarios. A proof-of-concept is available in the GitHub PoC Repository for security researchers to analyze the exploitation mechanism.

Detection Methods for CVE-2025-29329

Indicators of Compromise

• Unusual or malformed HTTP requests targeting the ippprint service on port 631 or the device's web interface
• Unexpected process crashes or restarts of the ippprint service
• Anomalous network traffic patterns originating from the router
• Unauthorized configuration changes on affected Sagemcom devices

Detection Strategies

• Monitor network traffic for HTTP requests with abnormally large payloads directed at the router's IPP service
• Implement intrusion detection rules to identify buffer overflow exploitation patterns in HTTP traffic
• Deploy network segmentation to isolate IoT and router management interfaces from untrusted networks
• Configure logging on upstream firewalls to capture and analyze traffic destined for vulnerable devices

Monitoring Recommendations

• Enable detailed logging for all administrative and service interfaces on affected routers
• Monitor for unexpected outbound connections from the router to unknown IP addresses
• Implement alerting for changes to router configuration or firmware
• Periodically audit firmware versions across all network devices to identify unpatched systems

How to Mitigate CVE-2025-29329

Immediate Actions Required

• Check if the ippprint service is enabled on affected Sagemcom F@st 3686 devices and disable it if not required
• Restrict access to the router's web interface and services to trusted internal networks only
• Ensure the router's management interface is not exposed to the internet
• Contact Sagemcom support or your ISP for firmware update availability

Patch Information

At the time of publication, no official patch information has been provided by Sagemcom. Users should monitor the Sagemcom Official Site for security advisories and firmware updates. ISP-provided routers should be updated through the service provider's managed update process when patches become available.

Workarounds

• Disable the ippprint (Internet Printing Protocol) service if network printing functionality is not required
• Implement firewall rules to block external access to the router's IPP service (typically port 631)
• Place the router behind an additional firewall or security appliance that can inspect and filter malicious traffic
• Consider replacing affected devices with alternative models if no patch is forthcoming

# Example firewall rule to block external IPP access (adjust for your environment)
iptables -A INPUT -p tcp --dport 631 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p udp --dport 631 -s ! 192.168.1.0/24 -j DROP