CVE-2026-5527 Overview
A hard-coded cryptographic key vulnerability has been identified in Tenda 4G03 Pro routers running firmware versions 1.0, 1.0re, 01.bin, and 04.03.01.53. The vulnerability exists within the ECDSA P-256 Private Key Handler component, specifically affecting the file /etc/www/pem/server.key. This security weakness allows remote attackers to potentially compromise the confidentiality of encrypted communications by exploiting the use of a hard-coded cryptographic key.
Critical Impact
Remote attackers can exploit the hard-coded ECDSA P-256 private key to decrypt TLS/SSL communications, potentially exposing sensitive data transmitted to and from the affected Tenda 4G03 Pro devices.
Affected Products
- Tenda 4G03 Pro firmware version 1.0
- Tenda 4G03 Pro firmware version 1.0re/01.bin
- Tenda 4G03 Pro firmware version 04.03.01.53
Discovery Timeline
- 2026-04-05 - CVE-2026-5527 published to NVD
- 2026-04-07 - Last updated in NVD database
Technical Details for CVE-2026-5527
Vulnerability Analysis
The vulnerability stems from the use of a hard-coded ECDSA P-256 private key embedded within the device firmware at the path /etc/www/pem/server.key. Hard-coded cryptographic keys represent a significant security weakness (CWE-320: Key Management Errors) because they remain constant across all deployed instances of the affected product. This means every Tenda 4G03 Pro device running the vulnerable firmware versions shares the same private key.
When a device uses a hard-coded private key for TLS/SSL communications, any attacker who obtains the key—either through firmware extraction, reverse engineering, or prior public disclosure—can decrypt intercepted traffic. The network-accessible nature of this vulnerability makes it particularly concerning, as attackers can passively capture encrypted communications and decrypt them offline.
Root Cause
The root cause of this vulnerability is a poor cryptographic key management practice where developers embedded a static ECDSA P-256 private key directly into the device firmware. Rather than generating unique cryptographic keys during device provisioning or first-time setup, the affected Tenda 4G03 Pro devices ship with identical key material stored in /etc/www/pem/server.key. This approach violates fundamental cryptographic security principles that require unique keys per device to ensure compromise of one device does not affect the security of others.
Attack Vector
The attack can be initiated remotely over the network without requiring any authentication or user interaction. An attacker would typically follow this attack methodology:
Key Extraction - The attacker extracts the hard-coded private key from the device firmware, which can be obtained from vendor update packages or by dumping firmware from a physical device.
Traffic Interception - The attacker positions themselves to capture TLS/SSL traffic between legitimate users and vulnerable Tenda 4G03 Pro devices through network sniffing or man-in-the-middle techniques.
Traffic Decryption - Using the extracted ECDSA P-256 private key, the attacker decrypts the captured communications, gaining access to sensitive data including credentials, configuration changes, and administrative commands.
The vulnerability allows for passive attacks where historical captured traffic can be decrypted, as well as active man-in-the-middle attacks where the attacker can impersonate the legitimate device.
Detection Methods for CVE-2026-5527
Indicators of Compromise
- Presence of known hard-coded private key material in firmware images or device file systems at /etc/www/pem/server.key
- TLS certificates presented by multiple Tenda 4G03 Pro devices containing identical public key fingerprints
- Unusual network reconnaissance activity targeting Tenda device management interfaces
Detection Strategies
- Conduct firmware analysis to identify the presence of hard-coded cryptographic key material in Tenda 4G03 Pro devices
- Implement network monitoring to detect TLS certificate anomalies where multiple devices present certificates with identical key fingerprints
- Deploy intrusion detection rules to identify potential man-in-the-middle attacks targeting vulnerable device communications
Monitoring Recommendations
- Monitor network traffic for unusual patterns indicating traffic interception or replay attacks against Tenda 4G03 Pro management interfaces
- Implement asset inventory tracking to identify all Tenda 4G03 Pro devices running vulnerable firmware versions
- Review TLS/SSL certificate configurations across deployed devices to identify shared key material
How to Mitigate CVE-2026-5527
Immediate Actions Required
- Identify all Tenda 4G03 Pro devices in your environment running firmware versions 1.0, 1.0re/01.bin, or 04.03.01.53
- Restrict network access to device management interfaces using firewall rules and network segmentation
- Avoid transmitting sensitive data through vulnerable devices until patched firmware is available
- Monitor the Tenda Official Website for security updates and patched firmware releases
Patch Information
At the time of publication, no vendor patch has been announced for this vulnerability. Organizations should monitor the VulDB Vulnerability Entry #355280 and the Tenda Official Website for updates regarding firmware releases that address this hard-coded key vulnerability. Additional technical details are available through the VulDB Submission #782053.
Workarounds
- Implement network segmentation to isolate vulnerable Tenda 4G03 Pro devices from sensitive network segments
- Deploy a VPN or additional encryption layer for communications that must traverse networks where these devices are present
- Consider replacing affected devices with alternative products that implement proper key generation and management practices
- Disable remote management interfaces if they are not required for operational purposes
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
