net-imap vulnerable to command Injection via unvalidated Symbol inputs

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.8 · 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 · score source

EPSS

• CVE-2026-42258: 0.78% estimated exploitation activity in the next 30 days; percentile 56.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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…

Published by the source

4 May 2026, 22:04 UTC

Last modified by the source

22 Jul 2026, 12:32 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-75xq-5h9v-w6px

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# Patch Next advisory brief: CVE-2026-42258

Advisory: net-imap vulnerable to command Injection via unvalidated Symbol inputs
IDs: CVE-2026-42258, GHSA-75xq-5h9v-w6px
Record: https://patchnext.com/advisories/cve-2026-42258 (revision 1, source checked 26 Oct 2026, 15:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: net-imap 0.6.4, 0.5.14, 0.4.24. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems net-imap: affected >= 0.6.0, <= 0.6.3; >= 0.5.0, <= 0.5.13; <= 0.4.23; fixed in 0.6.4, 0.5.14, 0.4.24

## Suggested inspection (read-only)
- RubyGems net-imap: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on net-imap.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-75xq-5h9v-w6px (GitHub-reviewed advisory GHSA-75xq-5h9v-w6px lists affected ranges: RubyGems net-imap >=0.6.0 =0.5.0 =0 <=0.4.23)

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