CVE-2026-42344

FastGPT: DNS rebinding TOCTOU bypass in isInternalAddress allows SSRF on all protected endpoints

State: Published
Severity: 6.3 Medium
Published: May 8, 2026
Updated: May 11, 2026
Reserved: Apr 26, 2026

Description

FastGPT is an AI Agent building platform. In versions 4.14.11 and prior, FastGPT's isInternalAddress() function in packages/service/common/system/utils.ts is vulnerable to DNS rebinding (TOCTOU — Time-of-Check to Time-of-Use). The function resolves the hostname via dns.resolve4()/dns.resolve6() and checks resolved IPs against private ranges, but the actual HTTP request happens in a separate call with a new DNS resolution, allowing the DNS record to change between validation and fetch. At time of publication, there are no publicly available patches.

Scores

CVSS	Score	Vector	Source
3.1	6.3 Medium	CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N	GitHub_M

Weaknesses

CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

Affected Products

Product	Versions
FastGPTlabring	<= 4.14.11Affected

References

https://github.com/labring/FastGPT/security/advisories/GHSA-cc8x-jrqv-hmwh

Every record here comes from the CVE Program’s CVE List. © 1999–2026 The MITRE Corporation. CVE is a registered trademark of The MITRE Corporation. The records are reproduced under the CVE Program terms of use.