# CVE-2026-71537: Paymenter has a credit-refund double-spend race condition in service downgrade (doUpgrade)

> CVE-2026-71537 (GitHub advisory GHSA-5gmm-hjfj-8ff7) is a medium-severity vulnerability with a CVSS 3.1 base score of 6.5, classed as Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') (CWE-362), in paymenter/paymenter (Packagist). Affected versions: <= 1.5.6. It is fixed in 1.5.7.

Canonical page: https://cveminer.com/vulnerabilities/CVE-2026-71537

| Field | Value |
| --- | --- |
| CVE | CVE-2026-71537 |
| GHSA | GHSA-5gmm-hjfj-8ff7 |
| Severity | Medium |
| CVSS 3.1 | 6.5 `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N` (GitHub Advisory Database) |
| CWE | CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') |
| EPSS | 0.23% (higher than 14% of CVEs) |
| CISA KEV | Not listed |
| Published | 18 Sept 2026 |
| Modified | 18 Sept 2026 |

## Description

The service downgrade implementation in `app/Livewire/Services/Upgrade.php::doUpgrade()` executes a proration calculation and a subsequent user credit refund without any transactional safety or database locks. The only concurrency check relies on an unisolated database query checking for existing pending upgrades. Because there is no active database transaction or pessimistic row-level lock spanning this validation and the subsequent credit update, concurrent downgrade requests can bypass the guard simultaneously. This allows a user to trigger multiple refunds for a single service downgrade.

##### Technical Details

The issue occurs because the application verifies eligibility using an unlocked read operation (`Service::upgradable`) which checks if a pending upgrade row exists. Since there is no enclosing `DB::transaction` or `lockForUpdate()`, multiple requests sent in parallel can all query the database at the same millisecond, observe that no pending upgrade exists, and pass the safety check.

Once passed, each concurrent request inserts its own pending upgrade record and executes `$credit->increment('amount', abs($price))`. Because the balance updates are not serialized against the initial check, the user's credit balance is cumulatively inflated by $N$ times the refund amount for a single legitimate downgrade.

##### Impact

This race condition allows any authenticated customer with an active, downgradable service to inflate their spendable credit balance to an arbitrary multiple of their legitimate refund amount.

Because the newly granted balance acts as real, spendable store credit, it can be immediately leveraged to settle future platform invoices or provision additional services, resulting in direct financial and resource loss to the operator.

## Affected packages

| Package | Ecosystem | PURL | Vulnerable versions | Fixed in |
| --- | --- | --- | --- | --- |
| paymenter/paymenter | Packagist | `pkg:composer/paymenter/paymenter` | <= 1.5.6 | 1.5.7 |

## Fix commits

- Patch: https://github.com/Paymenter/Paymenter/commit/a42e7f8bafce054ad70de3a2c2ac94d13579f41b
- Release: https://github.com/paymenter/paymenter/commit/f8a884e670e9b9e5efb59ab5a7c606bf058b17d7 (1.5.7)

## Questions

**What is the GHSA ID for CVE-2026-71537?**

GitHub tracks CVE-2026-71537 as GHSA-5gmm-hjfj-8ff7.

**What is the CVSS score of CVE-2026-71537?**

CVE-2026-71537 has a CVSS 3.1 base score of 6.5 (Medium), vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N.

**Which versions are affected by CVE-2026-71537?**

paymenter/paymenter (Packagist): <= 1.5.6.

**How do I fix CVE-2026-71537?**

Upgrade to 1.5.7 or later. The fix is in commit a42e7f8.

**What is the Package URL (PURL) for CVE-2026-71537?**

The affected package's PURL is pkg:composer/paymenter/paymenter.

**Is CVE-2026-71537 exploited in the wild?**

CISA's Known Exploited Vulnerabilities catalog doesn't list CVE-2026-71537. That means no confirmed exploitation has been catalogued, not that it is safe to leave unpatched. EPSS estimates a 0.23% chance of exploitation in the next 30 days, higher than 14% of CVEs.

## References

- https://github.com/Paymenter/Paymenter/commit/a42e7f8bafce054ad70de3a2c2ac94d13579f41b (fix)
- https://github.com/Paymenter/Paymenter/security/advisories/GHSA-5gmm-hjfj-8ff7 (advisory)
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71537.json (advisory)
- https://nvd.nist.gov/vuln/detail/CVE-2026-71537 (advisory)
- https://github.com/advisories/GHSA-5gmm-hjfj-8ff7 (advisory)
- https://github.com/Paymenter/Paymenter (package)
- https://github.com/Paymenter/Paymenter/releases/tag/v1.5.7

---

Source: CVEminer (https://cveminer.com/vulnerabilities/CVE-2026-71537), compiled from OSV (GitHub advisory), GitHub Advisory Database, OSV (CVE record), CVE.org, CISA KEV catalog. OSV and GitHub Advisory Database content is licensed CC BY 4.0.