CVE-2023-43644: Improper authentication in the SOCKS5 inbound in sing-box

Severity: critical (CVSS 9.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-09-25 · updated 2026-06-17
Weakness: CWE-306

Description

Sing-box is an open source proxy system. Affected versions are subject to an authentication bypass when specially crafted requests are sent to sing-box. This affects all SOCKS5 inbounds with user authentication and an attacker may be able to bypass authentication. Users are advised to update to sing-box 1.4.4 or to 1.5.0-rc.4. Users unable to update should not expose the SOCKS5 inbound to insecure environments.

Affected products

SagerNet sing-box: before 1.4.5; 1.5.0-beta1, 1.5.0-beta10, 1.5.0-beta11, 1.5.0-beta12, 1.5.0-beta2, 1.5.0-beta3 (+9) — fixed in 1.4.5

How to fix

Upgrade to a fixed version: SagerNet sing-box 1.4.5. Check the vendor advisory for mitigations.

References

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