CVE-2026-47240
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\n" 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\n" 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 on
CSIRTS triage
- What
- There is a command injection vulnerability via a non-synchronizing literal in the 'raw' argument.
- Who is affected
- Deployments using Net::IMAP are affected.
- Urgency
- Remediation is necessary as the severity is unknown and exploitation could lead to command execution.
- Action
- Update to a patched version of Net::IMAP.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.49% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 39% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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