CVE-2021-32066 in JD Edwards EnterpriseOne Tools
Summary
by MITRE • 08/02/2021
An issue was discovered in Ruby through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1. Net::IMAP does not raise an exception when StartTLS fails with an an unknown response, which might allow man-in-the-middle attackers to bypass the TLS protections by leveraging a network position between the client and the registry to block the StartTLS command, aka a "StartTLS stripping attack."
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Analysis
by VulDB Data Team • 05/09/2026
The vulnerability identified as CVE-2021-32066 represents a critical security flaw in Ruby's Net::IMAP implementation that undermines the integrity of TLS encryption protocols. This issue affects Ruby versions through 2.6.7, 2.7.x through 2.7.3, and 3.x through 3.0.1, creating a significant risk for applications that rely on secure email communication through IMAP protocols. The flaw specifically manifests in the handling of StartTLS negotiation, where the library fails to properly validate server responses during the secure connection establishment process.
The technical root cause of this vulnerability lies in the improper exception handling within Net::IMAP's StartTLS implementation. When a client attempts to establish a secure connection through StartTLS, the library should verify that the server responds appropriately to the TLS negotiation request. However, in the affected Ruby versions, if an unknown or unexpected response is received from the server, the system does not raise an exception as it should. This failure to validate responses creates a window where malicious actors can intercept communications and manipulate the TLS negotiation process. The vulnerability is particularly dangerous because it allows for what is known as a "StartTLS stripping attack" where attackers can position themselves between the client and server to block or manipulate the StartTLS command, effectively downgrading the connection to an insecure plaintext state.
This vulnerability directly relates to CWE-310, which addresses cryptographic weaknesses in TLS implementations, and aligns with ATT&CK technique T1566, specifically the "Phishing" tactic where attackers exploit protocol weaknesses to bypass security measures. The operational impact of CVE-2021-32066 is substantial as it compromises the fundamental security guarantees that TLS is designed to provide. Applications using Ruby's Net::IMAP library for email communication become vulnerable to man-in-the-middle attacks where attackers can intercept, modify, or steal sensitive email data without detection. The vulnerability affects any system that relies on Ruby applications for secure email access, potentially exposing confidential communications, authentication credentials, and personal information stored in email accounts.
Organizations should immediately upgrade to Ruby versions that have patched this vulnerability, specifically Ruby 2.6.8, 2.7.4, or 3.0.2 and later. Additionally, system administrators should implement network monitoring to detect unusual StartTLS behavior and consider deploying additional security measures such as certificate pinning or explicit TLS version requirements. The mitigation strategy should include comprehensive testing of patched applications to ensure that StartTLS failures are properly handled and that appropriate exceptions are raised when unexpected server responses occur. Security teams should also review their incident response procedures to address potential exploitation of this vulnerability and conduct thorough vulnerability assessments across all Ruby-based email applications and services that may be exposed to this threat.