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The vulnerability stems from how TP-Link Archer C7 v5 and v5.8 routers handle administrator login authentication. When a user logs into the router’s web interface, the admin password is encrypted client-side using a 1024-bit RSA key before being transmitted to the device. This encryption is performed within the browser’s JavaScript environment, making the key and algorithm accessible to an attacker who can inspect the network traffic. The critical flaw lies in the use of RSA-1024, a cryptographic key size that is no longer considered secure against modern computational capabilities. An adjacent attacker on the same local network segment can passively intercept the network packets containing the encrypted password. Once captured, the attacker can perform either a brute-force attack or, more feasibly, use modern factorization algorithms to crack the 1024-bit RSA key. The RSA modulus can be factored using the General Number Field Sieve (GNFS) on commodity hardware, revealing the private key. With the private key, the attacker can decrypt the intercepted password hash and recover the plaintext administrator password. This grants the attacker full administrative access to the router, allowing them to modify device configurations, change firewall rules, redirect traffic, or establish persistent backdoors. The vulnerability affects all firmware builds of the Archer C7 v5 and v5.8 through build version 20220715, and a patch was made available on April 16, 2026.
dailycve form:
Platform: TP-Link Archer
Version: v5 and v5.8
Vulnerability : Inadequate Encryption Strength
Severity: High (CVSS 8.8)
date: 2026-04-16
Prediction: Patched April 16, 2026
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What Undercode Say:
Check if your router is vulnerable by verifying the build version Log into the router's web interface and navigate to System Tools > Firmware Upgrade Vulnerable builds are those with a date up to 20220715 Simulate packet capture of the encrypted password using tcpdump sudo tcpdump -i eth0 -w tplink_login.pcap -s 0 'host 192.168.0.1 and port 80' Extract the RSA-encrypted password from the captured packets using tshark tshark -r tplink_login.pcap -Y "http.request" -T fields -e http.file_data Example of a factorization attack using yafu to crack the RSA-1024 modulus (for educational purposes, replace N with the captured modulus) yafu "factor(N)" -threads 4 Decrypt the password using the recovered private key with openssl openssl rsautl -decrypt -inkey private_key.pem -in encrypted_password.bin -out plaintext_password.txt
Exploit:
An attacker on the same local network (adjacent network) uses a packet sniffer like Wireshark or tcpdump to capture the HTTP POST request sent during a login attempt. The request contains the “password” parameter which is the RSA-1024 encrypted string. The attacker then uses a factorization tool (e.g., CADO-NFS or yafu) to compute the prime factors of the RSA modulus, which is publicly exposed in the router’s JavaScript code. Once factored, the attacker constructs the private key and decrypts the captured password, gaining full administrative access to the router.
Protection from this CVE
Apply the security patch released by TP-Link on April 16, 2026, which replaces the client-side RSA-1024 encryption with a stronger, server-side cryptographic mechanism. If patching is not immediately possible, disable the web interface’s remote management and restrict access to the local network only. Use strong network segmentation to isolate the router’s administrative interface from untrusted adjacent devices. Implement a VPN for all remote administrative access, and monitor network traffic for unusual HTTP POST requests to the router’s login endpoint.
Impact
An unauthenticated adjacent attacker with the ability to intercept network traffic can perform cryptographic attacks against the RSA-1024 encryption to recover the plaintext administrator password. This leads to full administrative compromise of the router, allowing the attacker to modify device configuration, disable security controls, redirect network traffic, and use the router as a pivot point to further compromise the entire internal network.
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Sources:
Reported By: nvd.nist.gov
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