CVE-2021-3154 in Serv-U
Summary
by MITRE • 05/04/2021
An issue was discovered in SolarWinds Serv-U before 15.2.2. Unauthenticated attackers can retrieve cleartext passwords via macro Injection. NOTE: this had a distinct fix relative to CVE-2020-35481.
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Analysis
by VulDB Data Team • 05/07/2021
The vulnerability identified as CVE-2021-3154 affects SolarWinds Serv-U software versions prior to 15.2.2, representing a critical security flaw that enables unauthenticated attackers to extract cleartext passwords through macro injection techniques. This vulnerability specifically targets the macro processing functionality within the Serv-U application, creating an avenue for attackers to bypass authentication mechanisms and access sensitive credential information without requiring valid login credentials. The flaw demonstrates the dangerous implications of improper input validation and macro execution handling within enterprise file transfer solutions that store and manage user credentials.
The technical implementation of this vulnerability stems from insufficient sanitization of macro parameters within the Serv-U application's processing pipeline. Attackers can craft malicious macro commands that, when executed by the vulnerable software, trigger the retrieval and exposure of stored cleartext passwords. This represents a classic command injection vulnerability pattern where user-supplied input is improperly handled within the macro execution context. The flaw operates at the application layer and can be exploited remotely without authentication, making it particularly dangerous for organizations that rely on Serv-U for file transfer operations and credential management. The vulnerability aligns with CWE-94, which describes improper execution of dynamic code, and demonstrates how macro processing can become a vector for credential theft when proper input validation is absent.
The operational impact of CVE-2021-3154 extends beyond simple credential theft, as it provides attackers with unauthorized access to systems and resources protected by the compromised credentials. Organizations using affected versions of Serv-U face potential data breaches, lateral movement within networks, and unauthorized access to sensitive corporate information. The vulnerability's exploitation does not require authentication, meaning that attackers can immediately begin harvesting credentials from exposed systems without prior access. This characteristic significantly increases the attack surface and risk exposure for affected organizations, particularly those with Serv-U installations that are accessible from external networks. The vulnerability's relationship to the broader ATT&CK framework can be mapped to techniques such as credential access and privilege escalation, where attackers leverage exposed credentials to gain deeper system access and maintain persistence.
Organizations should immediately upgrade to Serv-U version 15.2.2 or later to address this vulnerability, as this represents the official patch provided by SolarWinds to resolve the macro injection flaw. Additional mitigations include implementing network segmentation to limit access to Serv-U installations, disabling unnecessary macro functionality where possible, and monitoring network traffic for suspicious macro execution patterns. Security teams should also conduct comprehensive audits of all Serv-U installations to identify potentially affected systems and ensure proper patch management procedures are in place. The vulnerability serves as a reminder of the critical importance of validating all input within macro processing environments and implementing robust security controls around credential storage and access mechanisms.