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Fencer Intel
low 3.7

CVE-2026-126068 json

Action Mailbox: Possible signature replay in Action Mailbox Mailgun ingress

published 7d ago modified yesterday also EUVD-2026-122860 , GHSA-5957-c7qm-m469

cvss
3.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 28%
public exploits
0
none known

Summary

Action Mailbox routes incoming emails to controller-like mailboxes for processing in Rails. Prior to 8.1.4.1 and 8.0.5.2, 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. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Patch / fix

  • rubygems actionmailbox 8.0.5.2, 8.1.4.1

Is CVE-2026-126068 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-126068 updated cvss 3.7

actionmailbox: Action Mailbox: Inbound email forgery via Mailgun webhook signature replay

  • Red Hat 3scale API Management Platform 2 3scale-amp2/zync-rhel9, 3scale-amp2/system-rhel8, 3scale-amp2/system-rhel9
    affected: workaround, no fix available, no fix planned “Out of support scope”
  • Red Hat Satellite 6 rubygem-actionmailbox 7.0.8.7-1.el9sat
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
yesterday

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 28% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
GitHub 3.1 3.7 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
rubygems actionmailbox
>=8.1.0.beta1, <8.1.4.1
<8.0.5.2
8.1.4.1
8.0.5.2

Affected products

  • rails rails

Classification

Weakness
  • CWE-294 Authentication Bypass by Capture-replay
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of rails/rails published their own advisory on GitHub. Reviewed sources take precedence over it.