What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-14 · updated 2026-09-30
• Weakness: CWE-208

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 products

• pay-rails pay: before 11.6.2

References

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

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