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GHSA-75xq-5h9v-w6px CVE-2026-42258

net-imap vulnerable to command Injection via unvalidated Symbol inputs

Medium RubyGems
Severity
0.0 / 10
Medium · CVSS 4.0
Exploit chance (EPSS)
0.78%
Chance of exploitation in the next 30 days. Higher than 56.04% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-77 Improper Neutralization of Special Elements used in a Command ('Command Injection')
CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection')
Fix
0.6.4
Upgrade net-imap to this version or later

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.

Affected versions

RubyGems

PackageVulnerableFixed in
net-imap
>= 0.6.0, < 0.6.4
0.6.4
net-imap
>= 0.5.0, < 0.5.14
0.5.14
net-imap
< 0.4.24
0.4.24

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

net-imap RubyGems → 0.6.4

bundler
bundle update net-imap # Gemfile: gem "net-imap", ">= 0.6.4"

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N

Attack vector
Local
Attack complexity
High
Attack requirements
Present
Privileges required
None
User interaction
Passive
Confidentiality (vulnerable system)
None
Integrity (vulnerable system)
High
Availability (vulnerable system)
Low
Confidentiality (subsequent systems)
None
Integrity (subsequent systems)
None
Availability (subsequent systems)
None

CVSS 3.1 5.3

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:L

Attack vector
Local
Attack complexity
High
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
Low

Weakness

CWE-77: Improper Neutralization of Special Elements used in a Command ('Command Injection')

The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

How to prevent it
  • Architecture and Design: If at all possible, use library calls rather than external processes to recreate the desired functionality.
  • Implementation: If possible, ensure that all external commands called from the program are statically created.
  • Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
  • Operation: Run time: Run time policy enforcement may be used in an allowlist fashion to prevent use of any non-sanctioned commands.
  • System Configuration: Assign permissions that prevent the user from accessing/opening privileged files.

CWE-93: Improper Neutralization of CRLF Sequences ('CRLF Injection')

The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

How to prevent it
  • Implementation: Avoid using CRLF as a special sequence.
  • Implementation: Appropriately filter or quote CRLF sequences in user-controlled input.

References

Advisories

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
GHSA-46q3-7gv7-qmgg
Net::IMAP: Command Injection via ID command argument
Medium Also affects net-imap
GHSA-c4fp-cxrr-mj66
Net::IMAP: Denial of Service via incomplete raw argument validation
Low Also affects net-imap
GHSA-8p34-64r3-mwg8
Net::IMAP: Command Injection via non-synchronizing literal in "raw" argument
Medium Also affects net-imap
GHSA-hm49-wcqc-g2xg
net-imap vulnerable to command Injection via "raw" arguments to multiple commands
Critical Also affects net-imap
GHSA-87pf-fpwv-p7m7
net-imap vulnerable to denial of service via high iteration count for `SCRAM-*` authentication
Medium Also affects net-imap
GHSA-q2mw-fvj9-vvcw
net-imap has quadratic complexity when reading response literals
High Also affects net-imap
GHSA-vcgp-9326-pqcp
net-imap vulnerable to STARTTLS stripping via invalid response timing
High Also affects net-imap
GHSA-j3g3-5qv5-52mj
net-imap rubygem vulnerable to possible DoS by memory exhaustion
Medium Also affects net-imap
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