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

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-26 · updated 2026-06-17
Weakness: CWE-290

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 products

yansongda pay: before 3.7.20 — fixed in 3.7.20

How to fix

Upgrade to a fixed version: yansongda pay 3.7.20. Check the vendor advisory for mitigations.

References

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