GHSA-72w7-mf9g-733p nono-py has proxy-only network fallback bypass on older Linux kernels

Q: Which versions are affected by GHSA-72w7-mf9g-733p?

2 open source packages ship an affected version, including nono-py.

Q: Is GHSA-72w7-mf9g-733p being exploited?

There is no known exploitation of GHSA-72w7-mf9g-733p in the wild and no public exploit code.

Q: How do I fix GHSA-72w7-mf9g-733p?

Upgrade nono-py to 0.10.1 or later.

Not scored Published 26 Jun 2026

Attackers can bypass proxy-only network restrictions in nono-py on older Linux kernels to access cloud metadata endpoints and retrieve credentials.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is GHSA-72w7-mf9g-733p?

GHSA-72w7-mf9g-733p is a vulnerability in nono-py, published on 26 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Summary

On Linux kernels that do not support Landlock network rules, nono_py.sandboxed_exec() could run CapabilitySet.proxy_only(proxy) without supervising the seccomp-notify proxy-only fallback returned by the Rust core.

In that configuration, a sandboxed child process could remove HTTP_PROXY / HTTPS_PROXY environment variables or use raw sockets and then open direct TCP connections that should have been denied by proxy-only policy.

The issue affects proxy-only enforcement. It does not mean that all nono-py network blocking is ineffective. ECS validation showed caps.block_network() denied regular TCP and ECS metadata TCP on the tested Linux 6.1 host.

Impact

The intended proxy_only() security property is:

child processes may connect only to the local nono proxy port
the proxy enforces host allowlists and metadata/link-local denial
direct TCP to any other target is denied

Before the fix, on kernels without Landlock AccessNet, the Python binding applied the sandbox and then executed the child, but did not install and supervise the proxy-only seccomp-notify fallback. A child could therefore bypass the proxy layer in that old-kernel path.

The highest-impact scenario is a sandboxed workload with access to cloud metadata discovery inputs, where direct TCP to a metadata endpoint could retrieve task or instance credentials after proxy environment variables are removed.

Affected Conditions

The issue requires all of the following:

Linux runtime.
Kernel without Landlock network support, such as Linux 6.1. Landlock network rules require Landlock ABI v4 / Linux 6.7 or newer.
nono_py.sandboxed_exec() is used.
The capability set uses caps.proxy_only(proxy).
The child process removes or ignores proxy environment variables, or uses raw sockets.

macOS Seatbelt proxy-only enforcement is not affected by this Linux seccomp-notify fallback issue.

Affected Versions

Known affected builds include nono-py versions that expose and use CapabilitySet.proxy_only() through sandboxed_exec() before the supervised fallback fix in this working tree.

Earlier versions that did not expose CapabilitySet.proxy_only() are not affected by this specific proxy-only enforcement bug, though they may have separate environment-inheritance risks if callers passed broad parent environment variables into sandboxed children.

CVSS Score Rationale

Metric	Value	Rationale
Attack Vector (AV)	L — Local	Exploit is performed by a local process (unsetting env vars or opening raw sockets). Not remotely triggerable.
Attack Complexity (AC)	H — High	All of the following must be true: Linux runtime; kernel < 6.7 (no Landlock ABI v4); `sandboxed_exec()` used; capability set calls `proxy_only()`; child actively bypasses proxy env vars or uses raw sockets.
Privileges Required (PR)	L — Low	Attacker is already executing code inside the sandbox — some user-level privilege is required to get there.
User Interaction (UI)	N — None	No action from a user or operator is needed once the sandboxed child is running.
Scope (S)	C — Changed	The exploit crosses the sandbox security boundary, allowing the child to reach network resources outside the defined policy scope.
Confidentiality (C)	H — High	Highest-impact path: direct TCP to cloud metadata endpoint (169.254.169.254) yields IAM / task credentials.
Integrity (I)	L — Low	Attacker can make arbitrary outbound requests; no direct data modification from the bypass itself, but lateral credential use creates indirect risk.
Availability (A)	N — None	No denial-of-service impact described or implied.

Which versions are affected by GHSA-72w7-mf9g-733p?