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GHSA-75xq-5h9v-w6px

MediumCVSS 5.3 / 10

Published May 4, 2026·Last modified Jul 21, 2026

Affected Components(0)

No affected components available

Description

Summary

Symbol arguments to commands are vulnerable to a CRLF Injection / IMAP Command injection via Symbol arguments passed to IMAP commands.

Details

Symbol arguments represent IMAP "system flags", which are formatted as "atoms" (with no quoting) with a "\" prefix. Vulnerable versions of Net::IMAP sends the symbol name directly to the socket, with no validation.

Because the Symbol input is unvalidated, it could contain invalid flag characters, including SP and CRLF, which could be used to finish the current command and inject new commands.

Although IMAP flag arguments are only valid input for a few IMAP commands, most Net::IMAP commands use generic argument handling, and will allow Symbol (flag) inputs.

Note also that the list of valid symbol inputs should be restricted to an enumerated set of standard RFC defined flag types, which have each been given specific defined semantics. Any user-provided values outside of that list of standard "system flags" needs to use the IMAP keyword syntax, which are sent as atoms, i.e: string inputs. Under no circumstances should #to_sym ever be called on unvetted user-provided input: that will always be a bug in the calling code for the simple reason that user_input_atom is as \user_input_atom.

For forward compatibility with future IMAP extentions, Net::IMAP, does not restrict flag inputs to an enumerated list. That is the responsibility of the calling application code, which knows which flag semantics are valid for its context.

Impact

If a developer passes user-controlled input as a Symbol to most Net::IMAP commands, an attacker can append CRLF sequence followed by a new IMAP command (like DELETE mailbox).

Mitigation

Upgrade to a version of Net::IMAP that validates Symbols are valid as an IMAP flag.
User-provided input should never be able to control calling #to_sym on string arguments.

For example, do not unsafely serialize and deserialize command arguments (e.g. with YAML or Marshal) in a way that could create unvetted Symbol arguments.
For the few IMAP commands which do allow flag arguments, it may be appropriate to hard-code Symbol arguments or restrict them to an enumerated list which is valid for the calling application.

Risk Scores

Base Score

5.3

The vulnerability requires local access to the device to be exploited. It is difficult for an attacker to exploit this vulnerability and may require special conditions. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the integrity of the data. There is a low impact on the availability of the system.

Threat Intelligence

4.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS

0.78%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit

Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

Browse More

Medium severity

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