CVE-2026-42257 net-imap: Command Injection via "raw" arguments to multiple commands
Attackers can inject arbitrary IMAP commands via raw string arguments in the Ruby net-imap library if input is user-controlled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-42257?
CVE-2026-42257 is a medium-severity command injection vulnerability in ruby net-imap, published on 9 May 2026. It can only be exploited from the same machine or local network, 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, several Net::IMAP commands accept a raw string argument that is sent to the server without validation or escaping. If this string is derived from user-controlled input, it may contain contain CRLF sequences, which an attacker can use to inject arbitrary IMAP commands. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.
Which versions are affected by CVE-2026-42257?
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-2026-42257?
Upgrade net-imap to a fixed version for your release line: 0.4.24, 0.5.14 or 0.6.4.
Upgrade, and pass arguments to programs as a list instead of through a shell. More about Command injection.
Is CVE-2026-42257 being exploited?
There is no known exploitation of CVE-2026-42257 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-2026-42258 net-imap: Command Injection via unvalidated Symbol inputs
- CVE-2026-42245 net-imap: Quadratic complexity when reading response literals
Sources
Also known as ALPINE-CVE-2026-42257, BELL-CVE-2026-42257, CLEANSTART-2026-NN77724, CLEANSTART-2026-SU72949, CLSA-2026-1791456473, DEBIAN-CVE-2026-42257 and 22 more.