# 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.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2026
- **Updated:** 14 Sep 2026
- **Also known as:** GHSA-mjgf-xj26-9qf9

## 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 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-70658?

2 open source packages ship an affected version, including pay.


| Package | Ecosystem | 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-70658 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-70658 exists.

Affected packages and fixed versions:
- pay (RubyGems): affected all versions up to 11.6.1; no fix listed
- pay (RubyGems): affected all versions up to 11.6.1; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-70658/ (Markdown: https://insights.sbomify.com/CVE-2026-70658/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-70658
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-70658
- OSV: https://osv.dev/vulnerability/CVE-2026-70658

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-70658/
Summaries are generated and may contain mistakes; the official description above is the record.