How severe is CVE-2026-45755?

No CVSS score has been assigned to CVE-2026-45755 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-45755?

CVE-2026-45755 affects the following packages: symfony/mailtrap-mailer (Packagist), symfony/mailtrap-mailer (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-45755?

Update symfony/mailtrap-mailer to 7.4.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45755 is resolved across your whole dependency graph.

How do I detect CVE-2026-45755 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/mailtrap-mailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-45755 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-45755 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-45755 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-45755?

CVE-2026-45755 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 17th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-45755?

CVE-2026-45755 is classified as Missing Authentication (CWE-306), CWE-347 (CWE-347). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-45755 published, and has it been updated?

CVE-2026-45755 was published on July 14, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-45755 — mailtrap-mailer

Fix: symfony/symfony@4e0467e

CVE-2026-45755 is a Missing Authentication vulnerability in symfony/mailtrap-mailer. A fix is available for symfony/mailtrap-mailer — see the affected versions and patch details below.

Symfony: Mailtrap Mailer Webhook Parser Never Verifies the X-Mt-Signature HMAC — Unauthenticated Webhook Event Injection

Also known asGHSA-59f3-vp2f-mp9w

Published

Jul 14, 2026

Updated

Aug 12, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Oct 5, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-45755.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs17th percentile — riskier than 17% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

4 pkgs affected

🐘symfony/mailtrap-mailer🐘symfony/mailtrap-mailer🐘symfony/symfony🐘symfony/symfony

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/mailtrap-mailer`	≥ 7.2.0&&< 7.4.12	7.4.12`composer require symfony/mailtrap-mailer:^7.4.12`
🐘Packagist	`symfony/mailtrap-mailer`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/mailtrap-mailer:^8.0.12`
🐘Packagist	`symfony/symfony`	≥ 7.2.0&&< 7.4.12	7.4.12`composer require symfony/symfony:^7.4.12`
🐘Packagist	`symfony/symfony`	≥ 8.0.0&&< 8.0.12	8.0.12`composer require symfony/symfony:^8.0.12`

Affected Products

1 product · 2 configurations

Application

symfonysensiolabs

≥ 8.0.0 && < 8.0.12

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for symfony/mailtrap-mailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/mailtrap-mailer to 7.4.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-45755 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### 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 re