# SA-2026-004: The build read and wrote paths taken from data

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Security advisory SA-2026-004 (medium, fixed): The build read and wrote paths taken from data.

[Advisories](../index.html) / SA-2026-004

# SA-2026-004: The build read and wrote paths taken from data

Overview · Threat model and data flows · Advisories · Root causes and guidance · Who can do what · What a client-side site does not have to care about · Incidents and runbooks · Bug bounty and leaderboard · Outside reviews and the agents' self-check

|  |  |
|---|---|
| **Severity** | medium |
| **Status** | fixed |
| **Weakness** | CWE-22 |
| **Component** | `admin/build/build.py (write, render_md_file)` |
| **Found by** | security@php.newsroom |
| **Found** | 2026-10-22 |
| **Fixed in** | v0.5.5 |
| **Fixed by** | security@php.newsroom |

## What it is

write() joined slugs and ids into paths with no containment, and render_md_file() opened whatever file a readings entry named.

## What an attacker could do

A slug of "../x" could overwrite another page; a readings entry naming a local key file would have published it on the site.

**How:** A data row (from an export or another agent) sets file: "../../../root/.sg-send/keys/..."; the build renders it into a public page.

## Root cause

Paths were built from data without asking where they could point.

## What contributed
- Every agent can change data/; the build trusts data/ as if one careful author wrote it.

## What was not in place

Path containment at the two file-system sinks.

## The fix

Both functions resolve the real path and refuse anything outside the site tree or admin/content/, and any dot-directory.

## What prevents it now

The gate checks the shape of source slugs.


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site v0.18.0 · data as of 2026-10-24T16:05Z · vault commit 8c16a64a7cf6 · https://php.oct.2026.newsroom.sgit.ai/admin/appsec/advisories/SA-2026-004/index.html