Vulnerability · Published Sep 14, 2026 · Assigned by GitHub_M

CVE-2026-70658pay-rails/pay: non-constant-time HMAC comparison in Paddle Billing webhook signature verifier

High 7.4

In plain English

A high-severity security flaw in pay from pay-rails. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 48% of all known vulnerabilities).

Severity (CVSS 3.1)7.4High

Exploit odds (30 days)0.6%top 52.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Pay is a payments engine for Ruby on Rails 6.0 and higher. Prior to 11.6.2, Pay::Webhooks::PaddleBillingController#valid_signature? in app/controllers/pay/webhooks/paddle_billing_controller.rb compares the computed 64-character SHA-256 HMAC with the attacker-controlled h1 token from the Paddle-Signature header using Ruby String#==. An unauthenticated remote attacker who can repeatedly submit requests to /pay/webhooks/paddle_billing and obtain sufficiently precise timing measurements can infer matching digest prefixes and recover a valid signature. A forged accepted webhook is enqueued through Pay::Webhooks::ProcessJob and can cause a host application to update billing state, provision paid features, record refunds, or trigger customer notifications. This issue is fixed in version 11.6.2.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
RubyGems	pay	no fix listed	GHSA-mjgf-xj26-9qf9

Affected products (as reported)

Vendor	Product	Versions
pay-rails	pay	< 11.6.2

Weakness: CWE-208 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References

https://github.com/pay-rails/pay/security/advisories/GHSA-mjgf-xj26-9qf9 x_refsource_CONFIRM
https://github.com/pay-rails/pay/commit/ba6494109d88209fba2a4df2d9d6373fe81ed805 x_refsource_MISC
https://github.com/pay-rails/pay/releases/tag/v11.6.2 x_refsource_MISC