Summary
nono-py has proxy-only network fallback bypass on older Linux kernels
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.
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. |
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.
GHSA-72W7-MF9G-733P has a CVSS score of 6.4 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.10.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is GHSA-72W7-MF9G-733P? GHSA-72W7-MF9G-733P is a medium-severity security vulnerability in nono-py (pip), affecting versions >= 0.9.0, < 0.10.1. It is fixed in 0.10.1.
- How severe is GHSA-72W7-MF9G-733P? GHSA-72W7-MF9G-733P has a CVSS score of 6.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of nono-py are affected by GHSA-72W7-MF9G-733P? nono-py (pip) versions >= 0.9.0, < 0.10.1 is affected.
- Is there a fix for GHSA-72W7-MF9G-733P? Yes. GHSA-72W7-MF9G-733P is fixed in 0.10.1. Upgrade to this version or later.
- Is GHSA-72W7-MF9G-733P exploitable, and should I be worried? Whether GHSA-72W7-MF9G-733P is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-72W7-MF9G-733P is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-72W7-MF9G-733P? Upgrade
nono-pyto 0.10.1 or later.