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CVE-2026-42246— net-imap vulnerable to STARTTLS stripping via invalid response timing

Quick assessment

Affected
ruby net-imap
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Net::IMAP是Ruby开源的一个消息访问协议的 Ruby 客户端 api。 Net::IMAP 0.3.10之前版本、0.4.24之前版本、0.5.14之前版本和0.6.4之前版本存在安全漏洞，该漏洞源于中间人攻击者可使Net::IMAP#starttls返回成功而不启动TLS。

CVSS 7.6 · High EPSS 0.31% · P22

Possible ATT&CK Techniques 1 AI

T1557 · Adversary-in-the-Middle

Affected Version Matrix 4

VendorProduct Version RangeStatus
ruby net-imap < 0.3.10 affected
>= 0.4.0, < 0.4.24 affected
>= 0.5.0, < 0.5.14 affected
>= 0.6.0, < 0.6.4 affected
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I. Basic Information for CVE-2026-42246

Vulnerability Information
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Vulnerability Title
net-imap vulnerable to STARTTLS stripping via invalid response timing
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
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
Source: CVE Program / CVE List V5
Vulnerability Type
错误条件报告缺失
Source: CVE Program / CVE List V5
Vulnerability Title
Net::IMAP 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Net::IMAP是Ruby开源的一个消息访问协议的 Ruby 客户端 api。 Net::IMAP 0.3.10之前版本、0.4.24之前版本、0.5.14之前版本和0.6.4之前版本存在安全漏洞，该漏洞源于中间人攻击者可使Net::IMAP#starttls返回成功而不启动TLS。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
ruby net-imap < 0.3.10 -

II. Public POCs for CVE-2026-42246

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 11231 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
Full executable POC code
Exploit chain & mitigation
POC zip download
100+ AI POC generations per month

III. Intelligence Information for CVE-2026-42246

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Patches & Fixes for CVE-2026-42246 (5)

Vendor Advisories for CVE-2026-42246 (1)

Vendor Pages for CVE-2026-42246 (1)

Other References for CVE-2026-42246 (1)

Same Patch Batch · ruby · 2026-05-09 · 5 CVEs total

CVE-2026-42258 5.8 MEDIUM net-imap: Command Injection via unvalidated Symbol inputs
CVE-2026-42245 net-imap: Quadratic complexity when reading response literals
CVE-2026-42256 net-imap: Denial of service via high iteration count for `SCRAM-*` authentication
CVE-2026-42257 net-imap: Command Injection via "raw" arguments to multiple commands

IV. Related Vulnerabilities

Same product: net-imap
Same vendor: ruby
Same weakness: CWE-392

V. Comments for CVE-2026-42246

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