Vulnerability · Published Mar 26, 2026 · Assigned by GitHub_M

CVE-2026-33661WeChat Pay callback signature verification bypassed when Host header is localhost

High 8.6

In plain English

A high-severity authentication bypass by spoofing in pay from yansongda. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 44% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.6High

Exploit odds (30 days)0.5%top 55.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Pay is an open-source payment SDK extension package for various Chinese payment services. Prior to version 3.7.20, the `verify_wechat_sign()` function in `src/Functions.php` unconditionally skips all signature verification when the PSR-7 request reports `localhost` as the host. An attacker can exploit this by sending a crafted HTTP request to the WeChat Pay callback endpoint with a `Host: localhost` header, bypassing the RSA signature check entirely. This allows forging fake WeChat Pay payment success notifications, potentially causing applications to mark orders as paid without actual payment. Version 3.7.20 fixes the issue.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Packagist	yansongda/pay	3.7.20	GHSA-q938-ghwv-8gvc

Affected products (as reported)

Vendor	Product	Versions
yansongda	pay	< 3.7.20

Weakness: CWE-290 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N

References

https://github.com/yansongda/pay/security/advisories/GHSA-q938-ghwv-8gvc x_refsource_CONFIRM
https://github.com/yansongda/pay/commit/26987ebf789f1e7f0a85febb640986ab4289fd7f x_refsource_MISC
https://github.com/yansongda/pay/releases/tag/v3.7.20 x_refsource_MISC