TI-2026-26041 Aliases CVE-2026-33661 GHSA-q938-ghwv-8gvc

WeChat Pay callback signature verification bypassed when Host header is localhost

HIGH 76CWE-290Published 2026-03-26 · Updated 2026-03-27

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Security bypass
Confidentiality · integrity · availability: None · High · None
Fix status: Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-290.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00522 44th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

Fix Fixed pay (yansongda): 3.7.20yansongda/pay (Packagist): 3.7.20

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
yansongda	pay	before 3.7.20	3.7.20	Patch available	CNA
—	yansongda/pay (Packagist)	before 3.7.20	3.7.20	Patch available	GHSA-q938-ghwv-8gvc

pay Vendoryansongda Affected before 3.7.20 Fixed in 3.7.20 Patch available CNA
yansongda/pay (Packagist) Vendor— Affected before 3.7.20 Fixed in 3.7.20 Patch available GHSA-q938-ghwv-8gvc

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:yansongda:pay::::::::	before 3.7.20	Vulnerable	yansongda

cpe:2.3:a:yansongda:pay:*:*:*:*:*:*:*:* Versions before 3.7.20 Vulnerable ·yansongda

Remediation

Fix · CNA pay (yansongda) Fixed in 3.7.20
Fix · GHSA-q938-ghwv-8gvc yansongda/pay (Packagist) Fixed in 3.7.20 Advisory →

Timeline

2026-10-02 Threatist record created from CVE-2026-33661
2026-10-03 Alias added: GHSA-q938-ghwv-8gvc
2026-10-25 EPSS moved to the below the 50th percentile

References

Other 2

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences