CVE-2022-25219 in Phicomm
Summary
by MITRE • 03/10/2022
A null byte interaction error has been discovered in the code that the telnetd_startup daemon uses to construct a pair of ephemeral passwords that allow a user to spawn a telnet service on the router, and to ensure that the telnet service persists upon reboot. By means of a crafted exchange of UDP packets, an unauthenticated attacker on the local network can leverage this null byte interaction error in such a way as to make those ephemeral passwords predictable (with 1-in-94 odds). Since the attacker must manipulate data processed by the OpenSSL function RSA_public_decrypt(), successful exploitation of this vulnerability depends on the use of an unpadded RSA cipher (CVE-2022-25218).
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 03/12/2022
The vulnerability described in CVE-2022-25219 represents a critical security flaw in router firmware that affects the telnetd_startup daemon responsible for managing telnet service provisioning and persistence. This daemon generates ephemeral passwords to enable telnet access and ensure service continuity across reboots, creating a persistent attack surface that requires careful examination of cryptographic implementation details. The flaw manifests through a null byte interaction error within the password construction logic, which fundamentally compromises the randomness and unpredictability of these security credentials.
The technical exploitation pathway involves an attacker crafting specific UDP packet exchanges to manipulate data flowing through the OpenSSL RSA_public_decrypt() function, which operates on unpadded RSA cipher text. This creates a mathematical vulnerability where the null byte interaction error allows attackers to predict ephemeral passwords with a probability of 1-in-94, representing a significant reduction from the expected cryptographic randomness. The vulnerability specifically targets the cryptographic padding scheme used in RSA operations, where the absence of proper padding creates predictable patterns that can be exploited through statistical analysis and reverse engineering of the decryption process.
From an operational perspective, this vulnerability creates a persistent backdoor access mechanism for local network attackers who can leverage their position to manipulate router configuration and establish unauthorized persistent access to network infrastructure. The impact extends beyond simple credential compromise as the attacker gains the ability to maintain persistent telnet access across system reboots, effectively creating a long-term foothold within the network. This aligns with ATT&CK technique T1021.001 for remote services and T1078.004 for valid accounts, where the attacker can maintain access through legitimate service mechanisms that should remain protected.
The vulnerability demonstrates a classic cryptographic implementation flaw that falls under CWE-327, specifically addressing weak cryptographic algorithms and improper implementation of padding schemes. The error represents a failure in proper entropy generation and cryptographic key management, where the null byte interaction creates deterministic patterns in what should be random cryptographic values. Network security professionals must recognize this as a critical vulnerability requiring immediate attention, as it fundamentally undermines the trust model of router security and enables persistent unauthorized access to network infrastructure.
Mitigation strategies should focus on immediate firmware updates from vendors that address the cryptographic padding implementation and ensure proper entropy sources are utilized for password generation. Network segmentation and access controls should be implemented to limit local network exposure, while monitoring systems should be deployed to detect anomalous UDP packet patterns that might indicate exploitation attempts. Additionally, the vulnerability highlights the importance of proper cryptographic implementation practices and adherence to industry standards such as NIST SP 800-57 for key management and FIPS 186-4 for digital signature algorithms to prevent similar implementations that rely on insecure padding schemes.