What is CVE-2026-45755?

CVE-2026-45755 is a medium-severity missing authentication for critical function vulnerability in symfony/mailtrap-mailer (composer), affecting versions >= 7.2.0, < 7.4.12. It is fixed in 7.4.12, 8.0.12. A critical operation is accessible without requiring any authentication.

Which packages are affected by CVE-2026-45755?

symfony/mailtrap-mailer (composer) versions >= 7.2.0, = 7.2.0, < 7.4.12.

Is there a fix for CVE-2026-45755?

Yes. CVE-2026-45755 is fixed in 7.4.12, 8.0.12. Upgrade to this version or later.

Is CVE-2026-45755 exploitable, and should I be worried?

Whether CVE-2026-45755 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.

What actually determines whether CVE-2026-45755 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.

CVE-2026-45755 in symfony/mailtrap-mailer

Q: Which packages are affected by CVE-2026-45755?

symfony/mailtrap-mailer (composer) versions >= 7.2.0, = 7.2.0, < 7.4.12.

Q: Is there a fix for CVE-2026-45755?

Yes. CVE-2026-45755 is fixed in 7.4.12, 8.0.12. Upgrade to this version or later.

Q: Is CVE-2026-45755 exploitable, and should I be worried?

Whether CVE-2026-45755 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.

Q: What actually determines whether CVE-2026-45755 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.

Q: How do I fix CVE-2026-45755?

Upgrade: symfony/mailtrap-mailer to 7.4.12 or later, symfony/mailtrap-mailer to 8.0.12 or later, symfony/symfony to 7.4.12 or later, symfony/symfony to 8.0.12 or later.

Summary

Symfony's Mailtrap Mailer Webhook Parser Never Verifies the X-Mt-Signature HMAC, Unauthenticated Webhook Event Injection

Description

The Mailtrap mailer bridge ships a webhook request parser used to authenticate and decode the event callbacks Mailtrap POSTs to an application's webhook endpoint. Its doParse(Request $request, #[\SensitiveParameter] string $secret) method receives the configured webhook secret but never reads it; it decodes and returns the payload unconditionally, ignoring the X-Mt-Signature HMAC header Mailtrap sends with each request.

As a result, an application that wires up the Mailtrap webhook endpoint accepts any POST to that URL, even when a signing secret is configured (the recommended setup). An attacker who knows the endpoint exists can submit forged event payloads, fake delivery / bounce / open / click / spam events, leading to suppression-list corruption, delivery-metrics fraud, etc.

Resolution

MailtrapRequestParser::doParse() now requires and verifies the X-Mt-Signature header, an HMAC-SHA256 of the raw request body keyed with the configured secret, before decoding the payload, using a constant-time comparison.

When no secret is configured the behaviour is unchanged: signature verification remains opt-in, but it is now actually enforced once opted in.

The patch for this issue is available here for branch 7.4.

Credits

Symfony would like to thank Himanshu Anand for reporting the issue and Alexandre Daubois providing the fix.

Impact

A critical operation is accessible without requiring any authentication. Typical impact: any user can invoke the privileged function.

Affected versions

symfony/mailtrap-mailer (>= 7.2.0, < 7.4.12) symfony/mailtrap-mailer (>= 8.0.0, < 8.0.12) symfony/symfony (>= 7.2.0, < 7.4.12) symfony/symfony (>= 8.0.0, < 8.0.12)

Security releases

symfony/mailtrap-mailer → 7.4.12 (composer) symfony/mailtrap-mailer → 8.0.12 (composer) symfony/symfony → 7.4.12 (composer) symfony/symfony → 8.0.12 (composer)

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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Remediation advice

Upgrade the following packages to resolve this vulnerability:

symfony/mailtrap-mailer to 7.4.12 or later; symfony/mailtrap-mailer to 8.0.12 or later; symfony/symfony to 7.4.12 or later; symfony/symfony to 8.0.12 or later

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2026-45755? CVE-2026-45755 is a medium-severity missing authentication for critical function vulnerability in symfony/mailtrap-mailer (composer), affecting versions >= 7.2.0, < 7.4.12. It is fixed in 7.4.12, 8.0.12. A critical operation is accessible without requiring any authentication.
Which packages are affected by CVE-2026-45755?
- symfony/mailtrap-mailer (composer) (versions >= 7.2.0, < 7.4.12)
- symfony/symfony (composer) (versions >= 7.2.0, < 7.4.12)
Is there a fix for CVE-2026-45755? Yes. CVE-2026-45755 is fixed in 7.4.12, 8.0.12. Upgrade to this version or later.
Is CVE-2026-45755 exploitable, and should I be worried? Whether CVE-2026-45755 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-2026-45755 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-2026-45755?
- Upgrade symfony/mailtrap-mailer to 7.4.12 or later
- Upgrade symfony/mailtrap-mailer to 8.0.12 or later
- Upgrade symfony/symfony to 7.4.12 or later
- Upgrade symfony/symfony to 8.0.12 or later