Action Mailbox: Possible signature replay in Action Mailbox Mailgun ingress

Exploitation

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

CVSS

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

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Impact The Action Mailbox Mailgun ingress authenticates a request with an HMAC of the `timestamp` and `token` parameters concatenated without a separator, and `ActionMailbox::Ingresses::Mailgun::InboundEmailsController::Authenticator#recent?` rejects only timestamps more than 2 minutes in the past. Because the signature does not fix the boundary between the two values, a captured signed request can be presented with a timestamp far in the future, which the ingress then accepts indefinitely. An attacker who obtains one signed Mailgun webhook request, but not the signing key, could submit arbitrary inbound email that Action Mailbox processes as genuine, possibly leading to forged messages attributed to the sender of the attacker's choosing. Applications that receive inbound email through the Action Mailbox Mailgun ingress are affected.

Details The fixed releases also reject a Mailgun request whose timestamp is more than 2 minutes ahead of the server's clock, as they already did…

Published by the source

10 Nov 2026, 21:28 UTC

Last modified by the source

10 Nov 2026, 21:45 UTC

Source last checked

11 Nov 2026, 07:35 UTC

1. Revision 2 · amended · 11 Nov 2026

   Amended from osv record GHSA-5957-c7qm-m469

2. Revision 1 · created · 10 Nov 2026

   Published from ghsa record GHSA-5957-c7qm-m469

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# Patch Next advisory brief: CVE-2026-126068

Advisory: Action Mailbox: Possible signature replay in Action Mailbox Mailgun ingress
IDs: CVE-2026-126068, GHSA-5957-c7qm-m469
Record: https://patchnext.com/advisories/cve-2026-126068 (revision 2, source checked 11 Nov 2026, 07:35 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 3.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: actionmailbox 8.1.4.1, 8.0.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems actionmailbox: affected >= 8.1.0.beta1, < 8.1.4.1; < 8.0.5.2; fixed in 8.0.5.2, 8.1.4.1

## Suggested inspection (read-only)
- RubyGems actionmailbox: 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 actionmailbox.
- 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-5957-c7qm-m469 (GitHub-reviewed advisory GHSA-5957-c7qm-m469 lists affected ranges: RubyGems actionmailbox >=8.1.0.beta1 =0 <8.0.5.2)
- Verified: https://osv.dev/vulnerability/GHSA-5957-c7qm-m469 (OSV record GHSA-5957-c7qm-m469 lists affected ranges: RubyGems actionmailbox >=8.1.0.beta1 =0 <8.0.5.2 (fixed))

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