Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:NSummary
CVE-2026-33661 is a high-severity Authentication Bypass by Spoofing (CWE-290) vulnerability in Yansongda Pay. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Adversary-in-the-Middle (T1557); ranked at the 40th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to IA-2 (Identification and Authentication (Organizational Users)) and IA-3 (Device Identification and Authentication) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33661 affects the open-source Pay SDK, an extension package for integrating various Chinese payment services, including WeChat Pay. In versions prior to 3.7.20, the `verify_wechat_sign()` function in `src/Functions.php` bypasses all RSA signature verification if the PSR-7 HTTP request specifies `localhost` as the host header. This flaw, classified under CWE-290 (Authentication Bypass by Spoofing), carries a CVSS v3.1 base score of 8.6 (AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:N), highlighting its high severity due to network accessibility and scope change.
Any unauthenticated remote attacker can exploit this vulnerability by crafting an HTTP request to an application's WeChat Pay callback endpoint and setting the `Host` header to `localhost`. This tricks the SDK into skipping signature checks entirely, enabling the forgery of fake payment success notifications. Consequently, the target application may incorrectly process orders as paid, leading to potential financial losses without any actual payment from the customer.
The GitHub security advisory (GHSA-q938-ghwv-8gvc), release notes for v3.7.20, and the fixing commit (26987ebf789f1e7f0a85febb640986ab4289fd7f) confirm that upgrading to version 3.7.20 resolves the issue by addressing the unconditional localhost bypass in signature verification. Security practitioners should prioritize patching affected Pay SDK integrations and review callback endpoint configurations to prevent header spoofing.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16428
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 3 hardening rules · 3 OS baselines
V6.4.3V10.4.16V10.5.1V11.4.3
Mitigating Controls (NIST 800-53 r5) AI
Proper unique identification and authentication of users directly stops spoofing-based bypass of authentication.
Device identification and authentication before connection prevents spoofing of devices to bypass auth.
Authentication of non-organizational users blocks external spoofing attempts against the scheme.
Authenticator management ensures credentials cannot be easily spoofed or reused to bypass authentication.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Protecting, conveying, and verifying identity assertions specifically prevents the spoofing that enables authentication bypass.
Requiring authentication of users/services/hardware directly counters spoofing-based bypass when strong methods are used.
Proofing and binding identities reduces spoofing opportunities during enrollment but does not address runtime authentication implementation flaws.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Secure authentication control directly mitigates authentication bypass by spoofing.
Authentication information management directly addresses credential handling that prevents spoofing.
Security testing can detect spoofing vulnerabilities but does not prevent them by itself.
Access control policy reduces spoofing opportunities but does not prescribe authentication mechanisms.
Identity management supports unique identities but does not guarantee resistance to spoofing.
Access rights assignment limits exposure but does not enforce authentication strength.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (1 rule)
- V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-290
RHEL 7 (1 rule)
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-290
RHEL 8 (1 rule)
- V-230492 RHEL 8 must not have the rsh-server package installed. prevents CWE-290