CVE-2026-39418 MaxKB: SSRF via sandbox network hook bypass
Authenticated users can bypass sandbox network restrictions to access internal services via a socket flag bypass in MaxKB.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-39418?
CVE-2026-39418 is a medium-severity server-side request forgery vulnerability in 1Panel-dev MaxKB, published on 14 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
MaxKB is an open-source AI assistant for enterprise. In versions 2.7.1 and below, sandbox network protection can be bypassed by using socket.sendto() with the MSG_FASTOPEN flag. This allows authenticated user with tool-editing permissions to reach internal services that are explicitly blocked by the sandbox's banned hosts configuration. MaxKB's sandbox uses LD_PRELOAD to hook the connect() function and block connections to banned IPs, but Linux's sendto() with the MSG_FASTOPEN flag can establish TCP connections directly through the kernel without ever calling connect(), completely bypassing the IP validation. Although sendto is listed in the syscall() wrapper, this is ineffective because glibc invokes the kernel syscall directly rather than routing through the hooked syscall() function. This issue has been fixed in version 2.8.0.
Weakness: CWE-918
Which versions are affected by CVE-2026-39418?
It affects 1 product.
Products include Maxkb Maxkb.
How do I fix CVE-2026-39418?
No fix has been published for CVE-2026-39418 yet. Limit exposure of the affected software until one is available.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-39418 being exploited?
There is no known exploitation of CVE-2026-39418 in the wild and no public exploit code.
Other vulnerabilities in 1Panel-dev MaxKB
- CVE-2025-66419 MaxKB vulnerable to privilege escalation through sandbox bypass
- CVE-2025-66446 MaxKB has a Python sandbox LD_PRELOAD bypass
- CVE-2025-64511 MaxKB has SSRF in sandbox
- CVE-2026-39422 MaxKB has Stored XSS via ChatHeadersMiddleware
- CVE-2026-39423 Stored XSS via Eval Injection in EchartsRander Component
Sources
Also known as GHSA-w9g4-q3gm-6q6w.