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CVE-2026-42256— net-imap: Denial of service via high iteration count for `SCRAM-*` authentication

Quick assessment

Affected
ruby net-imap
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
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 0.4.0版本至0.4.24之前版本、0.5.0版本至0.5.14之前版本和0.6.0版本至0.6.4之前版本存在安全漏洞，该漏洞源于使用SCRAM-SHA1或SCRAM-SHA256认证连接时，恶意服务器可发送大迭代计数值导致计算型拒绝服务攻击。

AI Predicted 6.5 Difficulty: Easy EPSS 0.52% · P42

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 3

VendorProduct Version RangeStatus
ruby net-imap >= 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-2026-42256

Vulnerability Information
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Vulnerability Title
net-imap: Denial of service via high iteration count for `SCRAM-*` authentication
Source: CVE Program / CVE List V5
Vulnerability Description
Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. From versions 0.4.0 to before 0.4.24, 0.5.0 to before 0.5.14, and 0.6.0 to before 0.6.4, when authenticating a connection with SCRAM-SHA1 or SCRAM-SHA256, a hostile server can perform a computational denial-of-service attack on the client process by sending a big iteration count value. This issue has been patched in versions 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:N/VI:N/VA:H/SC:N/SI:N/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1322
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 0.4.0版本至0.4.24之前版本、0.5.0版本至0.5.14之前版本和0.6.0版本至0.6.4之前版本存在安全漏洞，该漏洞源于使用SCRAM-SHA1或SCRAM-SHA256认证连接时，恶意服务器可发送大迭代计数值导致计算型拒绝服务攻击。
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 >= 0.4.0, < 0.4.24 -

II. Public POCs for CVE-2026-42256

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III. Intelligence Information for CVE-2026-42256

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Patches & Fixes for CVE-2026-42256 (4)

Vendor Advisories for CVE-2026-42256 (1)

Vendor Pages for CVE-2026-42256 (1)

Other References for CVE-2026-42256 (1)

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

CVE-2026-42246 7.6 HIGH net-imap vulnerable to STARTTLS stripping via invalid response timing
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-2026-42257 net-imap: Command Injection via "raw" arguments to multiple commands

IV. Related Vulnerabilities

Same product: net-imap
Same vendor: ruby
Same weakness: CWE-1322

V. Comments for CVE-2026-42256

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