CVE-2022-25218 in Phicomm
Summary
by MITRE • 03/10/2022
The use of the RSA algorithm without OAEP, or any other padding scheme, in telnetd_startup, allows an unauthenticated attacker on the local area network to achieve a significant degree of control over the "plaintext" to which an arbitrary blob of ciphertext will be decrypted by OpenSSL's RSA_public_decrypt() function. This weakness allows the attacker to manipulate the various iterations of the telnetd startup state machine and eventually obtain a root shell on the device, by means of an exchange of crafted UDP packets. In all versions but K2 22.5.9.163 and K3C 32.1.15.93 a successful attack also requires the exploitation of a null-byte interaction error (CVE-2022-25219).
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Analysis
by VulDB Data Team • 03/12/2022
The vulnerability described in CVE-2022-25218 represents a critical cryptographic flaw within the telnetd startup process that exposes devices to remote code execution attacks. This weakness specifically targets the implementation of RSA encryption without proper padding mechanisms, creating a dangerous attack surface that allows unauthenticated adversaries to manipulate cryptographic operations and gain unauthorized system access. The vulnerability affects multiple device versions and demonstrates how improper cryptographic implementation can lead to complete system compromise, particularly when combined with additional exploitation vectors.
The technical flaw stems from the use of RSA algorithm without OAEP (Optimal Asymmetric Encryption Padding) or any other standardized padding scheme during the telnetd startup process. This implementation flaw allows attackers to exploit the RSA_public_decrypt() function in OpenSSL by crafting specific ciphertext blobs that, when decrypted, can manipulate the telnetd startup state machine iterations. The absence of proper padding creates a deterministic encryption scenario where attackers can predict and manipulate the plaintext output, fundamentally undermining the security guarantees that RSA encryption is designed to provide. This vulnerability directly relates to CWE-327, which addresses the use of weak or broken cryptographic algorithms, and CWE-780, which covers the use of RSA without proper padding.
The operational impact of this vulnerability extends beyond simple privilege escalation to full system compromise through a sophisticated attack chain involving crafted UDP packet exchanges. An unauthenticated attacker positioned within the local area network can leverage this weakness to manipulate the telnetd startup process and ultimately obtain root shell access to affected devices. The attack requires careful crafting of cryptographic parameters that exploit the deterministic nature of the flawed RSA implementation, allowing the attacker to control the decryption process and manipulate system state transitions. This represents a classic example of how cryptographic implementation flaws can be weaponized to achieve arbitrary code execution, with the attacker essentially controlling the plaintext that will be decrypted by the vulnerable OpenSSL function.
The exploitation scenario becomes more potent when combined with CVE-2022-25219, which addresses a null-byte interaction error that affects all versions except K2 22.5.9.163 and K3C 32.1.15.93. This additional vulnerability creates a more comprehensive attack vector that allows the attacker to achieve complete system compromise through the manipulation of both cryptographic padding and memory interaction errors. The combination of these two vulnerabilities demonstrates how seemingly isolated cryptographic weaknesses can compound to create devastating security implications, particularly in network services that rely on RSA encryption for authentication and key exchange processes.
Mitigation strategies for this vulnerability require immediate implementation of proper cryptographic padding mechanisms throughout the telnetd startup process, specifically implementing OAEP padding for all RSA operations. Network segmentation and access controls should be enforced to limit exposure to local network attackers, while implementing monitoring for unusual UDP packet patterns that may indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1072 for Software Deployment Tools and T1543 for Create or Modify System Process, as the exploitation involves manipulating system startup processes and cryptographic operations. Regular security updates and cryptographic audits should be implemented to prevent similar weaknesses in other network services and ensure proper padding schemes are enforced across all cryptographic implementations within the affected systems.