CVE-2026-42245 net-imap: Quadratic complexity when reading response literals
A malicious IMAP server can cause excessive CPU consumption in Ruby clients via crafted responses, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-42245?
CVE-2026-42245 is a low-severity denial of service vulnerability in ruby net-imap, published on 9 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.4.24, 0.5.14, and 0.6.4, Net::IMAP::ResponseReader has quadratic time complexity when reading large responses containing many string literals. A hostile server can send responses which are crafted to exhaust the client's CPU for a denial of service attack. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.
Weakness: CWE-407
Which versions are affected by CVE-2026-42245?
6 open source packages ship an affected version, including net-imap. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
net-imap RubyGems | All versions | 0.4.24 |
net-imap RubyGems | All versions | 0.4.24 |
net-imap RubyGems | From 0.5.0 | 0.5.14 |
net-imap RubyGems | From 0.5.0 | 0.5.14 |
net-imap RubyGems | From 0.6.0 | 0.6.4 |
net-imap RubyGems | From 0.6.0 | 0.6.4 |
Products include Ruby-Lang Net\.
How do I fix CVE-2026-42245?
Upgrade net-imap to a fixed version for your release line: 0.4.24, 0.5.14 or 0.6.4.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-42245 being exploited?
There is no known exploitation of CVE-2026-42245 in the wild and no public exploit code.
Other vulnerabilities in ruby net-imap
- CVE-2026-42246 net-imap vulnerable to STARTTLS stripping via invalid response timing
- CVE-2026-42256 net-imap: Denial of service via high iteration count for `SCRAM-*` authentication
- CVE-2025-43857 net-imap rubygem vulnerable to possible DoS by memory exhaustion
- CVE-2026-42257 net-imap: Command Injection via "raw" arguments to multiple commands
- CVE-2026-42258 net-imap: Command Injection via unvalidated Symbol inputs
Sources
Also known as ALPINE-CVE-2026-42245, BELL-CVE-2026-42245, CLEANSTART-2026-GP85472, CLEANSTART-2026-VQ04154, DEBIAN-CVE-2026-42245, ECHO-308f-3b2d-bb3e and 19 more.