net-imap vulnerable to STARTTLS stripping via invalid response timing

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Summary

CVECVE-2026-42246
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-09 20:16:28 UTC
Updated2026-05-09 20:16:28 UTC
DescriptionNet::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.

Risk And Classification

Primary CVSS: v4.0 7.6 HIGH from [email protected]

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary7.6HIGHCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED7.6HIGHCVSS: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 v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
Passive
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Ruby Net-imap affected < 0.3.10 Not specified
CNA Ruby Net-imap affected >= 0.4.0, < 0.4.24 Not specified
CNA Ruby Net-imap affected >= 0.5.0, < 0.5.14 Not specified
CNA Ruby Net-imap affected >= 0.6.0, < 0.6.4 Not specified

References

ReferenceSourceLinkTags
github.com/ruby/net-imap/commit/24a4e770b43230286a05aa2a9746cdbb3eb8485e [email protected] github.com
github.com/ruby/net-imap/releases/tag/v0.5.14 [email protected] github.com
github.com/ruby/net-imap/commit/f79d35bf5833f186e81044c57c843eda30c873da [email protected] github.com
github.com/ruby/net-imap/commit/0ede4c40b1523dfeaf95777b2678e54cc0fd9618 [email protected] github.com
github.com/ruby/net-imap/releases/tag/v0.4.24 [email protected] github.com
github.com/ruby/net-imap/releases/tag/v0.3.10 [email protected] github.com
github.com/ruby/net-imap/commit/97e2488fb5401a1783bddd959dde007d9fbce42c [email protected] github.com
github.com/ruby/net-imap/security/advisories/GHSA-vcgp-9326-pqcp [email protected] github.com
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