net-imap has quadratic complexity when reading response literals

Exploitation

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

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-42245: 0.41% estimated exploitation activity in the next 30 days; percentile 35.30 (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 Net::IMAP::ResponseReader has quadratic time complexity when reading large responses containing many string literals. A hostile server can send responses which are crafted to exhaust the client's CPU for a denial of service attack. Details For each literal in a response, ResponseReader rescans the entire growing response buffer. The regular expression that is used to scan the response buffer runs in linear time. With many literals, this becomes O(n²) total work. The regular expression should run in constant time: it is anchored to the end and only the last 23 bytes of the buffer are relevant. Because the algorithmic complexity is super-linear, this bypasses protection from maxresponsesize: a response can stay well below the default size limit while still causing very large CPU cost. Net::IMAP::ResponseReader runs continuously in the receiver thread until the connection closes. Impact This consumes disproportionate CPU time in the client's receiver thread. A hostile server…

Published by the source

4 May 2026, 22:02 UTC

Last modified by the source

14 May 2026, 20:48 UTC

Source last checked

26 Oct 2026, 15:52 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-q2mw-fvj9-vvcw

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# Patch Next advisory brief: CVE-2026-42245

Advisory: net-imap has quadratic complexity when reading response literals
IDs: CVE-2026-42245, GHSA-q2mw-fvj9-vvcw
Record: https://patchnext.com/advisories/cve-2026-42245 (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: Low (CVSS 2.3)
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-q2mw-fvj9-vvcw (GitHub-reviewed advisory GHSA-q2mw-fvj9-vvcw lists affected ranges: RubyGems net-imap >=0.6.0 =0.5.0 =0 <=0.4.23)

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