What is CVE-2026-48747?

CVE-2026-48747 is a medium-severity security vulnerability in symfony/mailomat-mailer (composer), affecting versions >= 7.2.0, < 7.4.13. It is fixed in 7.4.13, 8.0.13.

Which packages are affected by CVE-2026-48747?

symfony/mailomat-mailer (composer) versions >= 7.2.0, = 7.2.0, < 7.4.13.

Is there a fix for CVE-2026-48747?

Yes. CVE-2026-48747 is fixed in 7.4.13, 8.0.13. Upgrade to this version or later.

Is CVE-2026-48747 exploitable, and should I be worried?

Whether CVE-2026-48747 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-2026-48747 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-2026-48747 in symfony/mailomat-mailer

Q: Which packages are affected by CVE-2026-48747?

symfony/mailomat-mailer (composer) versions >= 7.2.0, = 7.2.0, < 7.4.13.

Q: Is there a fix for CVE-2026-48747?

Yes. CVE-2026-48747 is fixed in 7.4.13, 8.0.13. Upgrade to this version or later.

Q: Is CVE-2026-48747 exploitable, and should I be worried?

Whether CVE-2026-48747 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-2026-48747 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-2026-48747?

Upgrade: symfony/mailomat-mailer to 7.4.13 or later, symfony/mailomat-mailer to 8.0.13 or later, symfony/symfony to 7.4.13 or later, symfony/symfony to 8.0.13 or later.

Summary

Symfony: Mailomat Mailer Webhook Parser Reads the HMAC Algorithm from the Request: Signature Algorithm Downgrade

Description

Symfony\Component\Mailer\Bridge\Mailomat\Webhook\MailomatRequestParser::validateSignature() parses the X-MOM-Webhook-Signature request header as algo=signature and passes the wire-supplied $algo directly to hash_hmac() when verifying the request against the configured webhook secret. The request therefore selects the HMAC primitive used to authenticate it.

PHP's hash_hmac() enforces only that the chosen algorithm is HMAC-compatible. That set still includes primitives with known cryptanalysis (md4, md5, ripemd128, tiger128,3, …, e.g. existential forgery of HMAC-MD4, Contini & Yin, ASIACRYPT 2006). This is the canonical algorithm-confusion shape, analogous to JWT alg=none / alg=HS256 downgrades: any future cryptographic weakness in any HMAC primitive PHP exposes becomes immediately exploitable against a Mailomat webhook receiver, the moment an attacker is in a position to compute a signature for that primitive, without a code change on the Symfony side.

Mailomat's documented webhook security pins SHA-256; the parser did not.

Resolution

MailomatRequestParser::validateSignature() now requires the signature header to be of the form sha256=<hex> and verifies the signature with HMAC-SHA256 keyed by the configured secret using a constant-time comparison. Any other algorithm declared on the wire (including the HMAC primitives PHP would otherwise accept) is rejected.

The patch for this issue is available here for branch 7.4 (and forward-ported to 8.0 and 8.1).

Credits

Symfony would like to thank Omar Alshammari, Essam Alanazi and Alwaleed Alshammari for reporting the issue and Nicolas Grekas for providing the fix.

Impact

Affected versions

symfony/mailomat-mailer (>= 7.2.0, < 7.4.13) symfony/mailomat-mailer (>= 8.0.0, < 8.0.13) symfony/symfony (>= 7.2.0, < 7.4.13) symfony/symfony (>= 8.0.0, < 8.0.13)

Security releases

symfony/mailomat-mailer → 7.4.13 (composer) symfony/mailomat-mailer → 8.0.13 (composer) symfony/symfony → 7.4.13 (composer) symfony/symfony → 8.0.13 (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/mailomat-mailer to 7.4.13 or later; symfony/mailomat-mailer to 8.0.13 or later; symfony/symfony to 7.4.13 or later; symfony/symfony to 8.0.13 or later

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

Frequently Asked Questions

What is CVE-2026-48747? CVE-2026-48747 is a medium-severity security vulnerability in symfony/mailomat-mailer (composer), affecting versions >= 7.2.0, < 7.4.13. It is fixed in 7.4.13, 8.0.13.
Which packages are affected by CVE-2026-48747?
- symfony/mailomat-mailer (composer) (versions >= 7.2.0, < 7.4.13)
- symfony/symfony (composer) (versions >= 7.2.0, < 7.4.13)
Is there a fix for CVE-2026-48747? Yes. CVE-2026-48747 is fixed in 7.4.13, 8.0.13. Upgrade to this version or later.
Is CVE-2026-48747 exploitable, and should I be worried? Whether CVE-2026-48747 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-2026-48747 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-2026-48747?
- Upgrade symfony/mailomat-mailer to 7.4.13 or later
- Upgrade symfony/mailomat-mailer to 8.0.13 or later
- Upgrade symfony/symfony to 7.4.13 or later
- Upgrade symfony/symfony to 8.0.13 or later