PT-2026-48340 · Rubygems · Net::Imap

Published

2026-06-09

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Updated

2026-06-09

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CVE-2026-47240

CVSS v4.0

5.8

Medium

VectorAV:L/AC:L/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
Several Net::IMAP commands accept a "raw data" argument that is sent verbatim after validation to prevent command injection. However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals.

Details

Raw data arguments support embedded literal values, both synchronizing and non-synchronizing. Non-synchronizing literals can only be safely sent when the server advertises any of the LITERAL+, LITERAL-, or IMAP4rev2 capabilities. But raw data arguments do not verify server support for non-synchronizing literals prior to sending.
Servers without support for non-synchronizing literals could handle them in several different ways: If a server sees a "}r " byte sequence but can't parse the literal bytesize, it may cautiously decide to close the connection, blocking any command injection attacks. However, a server without support for non-synchronizing literals may instead interpret the "+}r " as the end of a malformed command line and respond with a tagged BAD. In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed.
This affects the following commands' string arguments:
  • criteria for #search and #uid search
  • search keys for #sort, #thread, #uid sort, and #uid thread
  • attr for #fetch and #uid fetch
Prior to net-imap v0.6.4, v0.5.14, and v0.4.24, raw data arguments were not validated in any way, so they were also vulnerable to this attack. See CVE-2026-42257 (GHSA-hm49-wcqc-g2xg).

Impact

Fortunately, LITERAL- is supported by most modern IMAP servers. Even without support for non-synchronizing literals, cautious servers may handle invalid literal bytesize by closing the connection . However, servers which handle a non-synchronizing literal just like any other malformed command will enable this vulnerability.
If a developer passes an unvalidated user-controlled input for one of these method arguments, an attacker can append CRLF sequence followed by a new IMAP command (like DELETE mailbox). Although this does not directly enable data exfiltration, it could be combined with other attack vectors or knowledge of the target system's attributes, e.g.: shared mail folders or the application's installed response handlers.

Mitigation

Update to a version of net-imap which validates server support for non-synchronizing literals before sending them.
If upgrading net-imap is not possible:
  • Explicitly validate user-controlled inputs to prevent embedded non-synchronizing literals unless the server supports them.
  • For a simpler, more cautious approach: all embedded literals can be unconditionally prohibited, by checking that string inputs do not contain any CR or LF bytes.
  • Verify that the server advertises any of the LITERAL+, LITERAL-, or IMAP4rev2 capabilities before using untrusted string inputs for the affected "raw data" arguments.

Fix

Command Injection

Weakness Enumeration

CWE-77CWE-93

Related Identifiers

CVE-2026-47240
GHSA-8P34-64R3-MWG8

Affected Products

Net::Imap