CVE-2026-42246 PUBLISHED

net-imap vulnerable to STARTTLS stripping via invalid response timing

Assigner: GitHub_M
Reserved: 25.04.2026 Published: 09.05.2026 Updated: 09.05.2026

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.3.10, 0.4.24, 0.5.14, and 0.6.4, a man-in-the-middle attacker can cause Net::IMAP#starttls to return "successfully", without starting TLS. This issue has been patched in versions 0.3.10, 0.4.24, 0.5.14, and 0.6.4.

Metrics

CVSS 4.0

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS Score: 7.6

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	High	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	Passive

CVSS 4.0

Product Status

Vendor	ruby
Product	net-imap
Versions	Version < 0.3.10 is affected Version >= 0.4.0, < 0.4.24 is affected Version >= 0.5.0, < 0.5.14 is affected Version >= 0.6.0, < 0.6.4 is affected

References

Problem Types

CWE-392: Missing Report of Error Condition CWE
CWE-393: Return of Wrong Status Code CWE
CWE-754: Improper Check for Unusual or Exceptional Conditions CWE
CWE-636: Not Failing Securely ('Failing Open') CWE
CWE-841: Improper Enforcement of Behavioral Workflow CWE