Summary
Symfony's Mailjet Mailer Webhook Parser Never Verifies the Configured Secret, Unauthenticated Webhook Event Injection
Description
The Mailjet mailer bridge and the LOX24 SMS notifier bridge both ship webhook request parsers used to authenticate and decode the event callbacks each provider POSTs to an application's webhook endpoint. Their doParse(Request $request, #[\SensitiveParameter] string $secret) methods receive the configured webhook secret but never read it; they convert and return the payload unconditionally.
As a result, an application that wires up either webhook endpoint accepts any POST to that URL, even when a webhook secret is configured (the recommended setup). An attacker who knows the endpoint exists can submit forged event payloads, fake bounce / blocked / spam / open / click / delivery events, leading to suppression-list corruption, delivery-metrics fraud, etc.
Resolution
MailjetRequestParser::doParse() now rejects the request unless it carries the expected HTTP Basic credentials, Mailjet's webhook authentication mechanism, using a constant-time comparison. The configured webhook secret is matched against the credentials embedded in the Mailjet webhook URL as user:password (use :password when the URL has no username).
Lox24RequestParser::doParse() now rejects the request unless it carries an X-LOX24-Token HTTP header whose value matches the configured secret, using a constant-time comparison. The same token must be configured in the LOX24 dashboard under the callback settings.
When no secret is configured the behaviour is unchanged: webhook authentication remains opt-in, but it is now actually enforced once opted in.
The Mailjet patch is available here for branch 6.4.
The LOX24 patch is available here for branch 7.4 (the LOX24 bridge was introduced in 7.1 and is not present in 6.4).
Credits
Symfony would like to thank Himanshu Anand for reporting the issue, and Alexandre Daubois and Nicolas Grekas for providing the fixes.
Impact
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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symfony/lox24-notifier to 7.4.12 or later; symfony/lox24-notifier to 8.0.12 or later; symfony/symfony to 6.4.40 or later; symfony/symfony to 7.4.12 or later; symfony/symfony to 8.0.12 or later; symfony/mailjet-mailer to 6.4.40 or later; symfony/mailjet-mailer to 7.4.12 or later; symfony/mailjet-mailer to 8.0.12 or later
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Frequently Asked Questions
- What is CVE-2026-45754? CVE-2026-45754 is a medium-severity improper authentication vulnerability in symfony/lox24-notifier (composer), affecting versions >= 7.1.0, < 7.4.12. It is fixed in 7.4.12, 8.0.12, 6.4.40. The application does not adequately verify the identity of a user, device, or process before granting access.
- Which packages are affected by CVE-2026-45754?
symfony/lox24-notifier(composer) (versions >= 7.1.0, < 7.4.12)symfony/symfony(composer) (versions >= 6.4.0, < 6.4.40)symfony/mailjet-mailer(composer) (versions >= 6.4.0, < 6.4.40)
- Is there a fix for CVE-2026-45754? Yes. CVE-2026-45754 is fixed in 7.4.12, 8.0.12, 6.4.40. Upgrade to this version or later.
- Is CVE-2026-45754 exploitable, and should I be worried? Whether CVE-2026-45754 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45754 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45754?
- Upgrade
symfony/lox24-notifierto 7.4.12 or later - Upgrade
symfony/lox24-notifierto 8.0.12 or later - Upgrade
symfony/symfonyto 6.4.40 or later - Upgrade
symfony/symfonyto 7.4.12 or later - Upgrade
symfony/symfonyto 8.0.12 or later - Upgrade
symfony/mailjet-mailerto 6.4.40 or later - Upgrade
symfony/mailjet-mailerto 7.4.12 or later - Upgrade
symfony/mailjet-mailerto 8.0.12 or later
- Upgrade