CVE-2026-33661
CWE-290Published: March 26, 2026· Updated: Apr 1, 2026
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.
Technical Analysis
CVE-2026-33661 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.
The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.
A successful exploit results in full integrity compromise (data manipulation), with a CVSS base score of 7.5.
CVSS v3.1 Vector Breakdown
Affected Vendors & Products
Exploit & PoC Resources
Official Patches & Advisories
All References (4)
Quick Facts
Related CVEs (CWE-290)
Recommended Actions
- →Apply vendor patches immediately
- →Monitor CVE-2026-33661 in threat intel feeds
- →Review IDS/IPS signatures for exploitation attempts