CVE-2017-0897 in ExpressionEngine
Summary
by MITRE
ExpressionEngine version 2.x < 2.11.8 and version 3.x < 3.5.5 create an object signing token with weak entropy. Successfully guessing the token can lead to remote code execution.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/29/2019
The vulnerability identified as CVE-2017-0897 affects ExpressionEngine content management systems across versions 2.x prior to 2.11.8 and 3.x prior to 3.5.5. This weakness resides in the object signing token generation mechanism that fails to produce sufficiently random values, creating predictable cryptographic tokens that can be exploited by malicious actors. The flaw represents a critical security issue that undermines the integrity of the application's authentication and authorization processes.
The technical implementation of this vulnerability stems from insufficient entropy in the random number generation algorithm used to create object signing tokens. These tokens serve as cryptographic signatures that validate user sessions and prevent unauthorized access to administrative functions. When entropy is weak, the randomness of generated tokens becomes predictable, allowing attackers to guess valid tokens through brute force or statistical analysis. The vulnerability specifically targets the session management component where these tokens are utilized for authentication purposes, making it particularly dangerous as it enables unauthorized users to impersonate legitimate administrators.
The operational impact of this vulnerability extends beyond simple privilege escalation to enable full remote code execution capabilities. An attacker who successfully guesses a valid object signing token can gain administrative access to the ExpressionEngine installation and execute arbitrary code on the affected server. This represents a severe compromise of system integrity and confidentiality, as the attacker can modify content, access sensitive data, install backdoors, or even use the compromised system as a launch point for further attacks within the network infrastructure. The vulnerability's exploitability is heightened by the fact that it requires no authentication to begin the attack process, making it particularly dangerous in environments where the application is publicly accessible.
This vulnerability maps directly to CWE-330 Use of Insufficiently Random Values and aligns with ATT&CK technique T1078 Valid Accounts, as it enables attackers to gain access to legitimate administrative accounts through predictable token generation. The weakness also corresponds to ATT&CK technique T1059 Command and Scripting Interpreter, since successful exploitation allows for remote code execution. Organizations should prioritize immediate patching of affected installations, implementing network segmentation to limit exposure, and monitoring for suspicious authentication attempts. The recommended mitigation strategy includes updating to ExpressionEngine versions 2.11.8 or 3.5.5, which contain proper random number generation implementations and strengthened cryptographic token creation mechanisms. Additionally, implementing additional security controls such as web application firewalls, rate limiting, and intrusion detection systems can provide defense-in-depth protection against exploitation attempts.