How severe is CVE-2026-48747?

No CVSS score has been assigned to CVE-2026-48747 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-48747?

CVE-2026-48747 affects the following packages: symfony/mailomat-mailer (Packagist), symfony/mailomat-mailer (Packagist), symfony/symfony (Packagist), symfony/symfony (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-48747?

Update symfony/mailomat-mailer to 7.4.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48747 is resolved across your whole dependency graph.

How do I detect CVE-2026-48747 in my Packagist dependencies?

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

How do I mitigate CVE-2026-48747 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-48747 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-48747 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-2026-48747?

CVE-2026-48747 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 15th 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-2026-48747?

CVE-2026-48747 is classified as CWE-347 (CWE-347), CWE-757 (CWE-757). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-48747 published, and has it been updated?

CVE-2026-48747 was published on July 14, 2026 and was last updated on October 22, 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-2026-48747 — mailomat-mailer

Fix: symfony/symfony@bdfe9fe

CVE-2026-48747 is a CWE-347 vulnerability in symfony/mailomat-mailer. A fix is available for symfony/mailomat-mailer — see the affected versions and patch details below.

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

Also known asGHSA-rrj9-5q2j-4gvr

Published

Jul 14, 2026

Updated

Oct 22, 2026

Affected

4 pkgs

Patched

4 / 4

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

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-2026-48747.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs15th percentile — riskier than 15% of all scored CVEsHighest risk

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

Real-World Exposure

4 pkgs affected

🐘symfony/mailomat-mailer🐘symfony/mailomat-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

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.

Affected Packages

4 total 4 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`symfony/mailomat-mailer`	≥ 7.2.0&&< 7.4.13	7.4.13`composer require symfony/mailomat-mailer:^7.4.13`
🐘Packagist	`symfony/mailomat-mailer`	≥ 8.0.0&&< 8.0.13	8.0.13`composer require symfony/mailomat-mailer:^8.0.13`
🐘Packagist	`symfony/symfony`	≥ 7.2.0&&< 7.4.13	7.4.13`composer require symfony/symfony:^7.4.13`
🐘Packagist	`symfony/symfony`	≥ 8.0.0&&< 8.0.13	8.0.13`composer require symfony/symfony:^8.0.13`

Affected Products

1 product · 2 configurations

Application

symfonysensiolabs

≥ 8.0.0 && < 8.0.13

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/mailomat-mailer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update symfony/mailomat-mailer to 7.4.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-48747 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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

O3 Security · Impact-Aware SCA

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CVE-2026-48747 — mailomat-mailer

Exploitation Status

No confirmed exploitation observed yet

EPSS Exploitation Probability

Real-World Exposure

Description

Description

Resolution

Credits

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2026-48747 in your dependencies?