CVE-2026-70658 pay-rails/pay: non-constant-time HMAC comparison in Paddle Billing webhook signature verifier
An attacker can bypass webhook signature verification via timing attacks to forge billing events, potentially granting unauthorized access to paid features or modifying customer data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-70658?
CVE-2026-70658 is a high-severity vulnerability in pay-rails pay, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-208
Which versions are affected by CVE-2026-70658?
2 open source packages ship an affected version, including pay.
| Package | Affected | Fixed in |
|---|---|---|
pay RubyGems | All versions to 11.6.1 | None |
pay RubyGems | All versions to 11.6.1 | None |
How do I fix CVE-2026-70658?
No fix has been published for CVE-2026-70658 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-70658 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-70658 exists.
Sources
Also known as GHSA-mjgf-xj26-9qf9.