---
id: "GHSA-5957-c7qm-m469"
page: "https://infrastack.ai/live/GHSA-5957-c7qm-m469"
kind: "vulnerability"
aliases: ["GHSA-5957-c7qm-m469"]
title: "Possible signature replay in Action Mailbox Mailgun ingress"
severity: "low"
cvss: 3.7
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "actionmailbox", "fixed": ["8.1.4.1"], "affected": ">= 8.1, < 8.1.4.1", "ecosystem": "rubygems"}, {"name": "actionmailbox", "fixed": ["8.0.5.2"], "affected": "< 8.0.5.2", "ecosystem": "rubygems"}]
ecosystems: ["rubygems"]
tags: ["action-mailbox", "cwe-294", "mailgun", "package", "rails", "self-hosted"]
not_affected_if: ["no-mailgun-ingress", "other-inbound-email-provider"]
published_at: "2026-11-04T03:02:01+00:00"
first_seen_at: "2026-11-09T22:53:29+00:00"
updated_at: "2026-11-09T22:57:17+00:00"
sources: [{"source": "ghsa-repo", "url": "https://github.com/rails/rails/security/advisories/GHSA-5957-c7qm-m469", "first_seen_at": "2026-11-09T22:53:29+00:00"}]
exploit_sources: []
---

# Possible signature replay in Action Mailbox Mailgun ingress

Link for people: https://infrastack.ai/live/GHSA-5957-c7qm-m469 (this .md is for agents)

Action Mailbox's Mailgun ingress signs the timestamp and token without a separator, so a captured signed webhook can be replayed with a future timestamp and accepted indefinitely. An attacker holding one signed Mailgun request could submit arbitrary inbound email that the app processes as genuine.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- rubygems:actionmailbox affected >= 8.1, < 8.1.4.1 fixed 8.1.4.1
- rubygems:actionmailbox affected < 8.0.5.2 fixed 8.0.5.2

## How to check

- Check the installed `actionmailbox` version in Gemfile.lock against the ranges below.
- Look for the Mailgun ingress in use: `config.action_mailbox.ingress = :mailgun` or a Mailgun route to `/rails/action_mailbox/mailgun/inbound_emails/mx`.

## Fix

- Rails `actionmailbox` 8.1 series: upgrade to `8.1.4.1`
- Rails `actionmailbox` 8.0 series: upgrade to `8.0.5.2`
- Patch commits for those who cannot upgrade at once are linked in the advisory (8.1 and 8.0).

## Timeline

- 2026-11-09T22:53:29+00:00 ghsa-repo https://github.com/rails/rails/security/advisories/GHSA-5957-c7qm-m469

## Documents

- [advisory] Maintainer's advisory: github.com https://github.com/rails/rails/security/advisories/GHSA-5957-c7qm-m469

## From the sources

### 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 for one more than 2 minutes behind it. An application whose clock runs more than 2 minutes behind Mailgun's will now reject genuine webhooks and should synchronize its clock.

### Releases
The fixed releases are available at the normal locations.

Patches for those who cannot upgrade at once:
- 8.1: https://github.com/rails/rails/commit/c3a295c5c22266e8ec4d0e664e6923a299235e7a.patch
- 8.0: https://github.com/rails/rails/commit/4aa2ec66822bc4eb8b341a0608f1c90a3e371a34.patch

### Credit
This issue was responsibly reported by HackerOne researcher [davutselcuk](https://hackerone.com/davutselcuk).

---

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