fix: escape user search term in getMyQuestions to prevent ReDoS

[ionfwsrijan]

Problem

GET /api/questions/my-questions compiles the q query param directly into a RegExp:

const searchRegex = new RegExp(q.trim(), "i");

A crafted term like (a+)+$ can trigger catastrophic backtracking when MongoDB evaluates the regex against large text fields, stalling the shared mongod process (ReDoS). The term is also unbounded in length, so arbitrarily long inputs create oversized regexes.

Fix

• Added an escapeRegex helper that escapes all regex metacharacters ([.*+?^${}()|[\]\\]), so the user term is matched as a literal substring instead of being interpreted as pattern syntax.
• Capped the search term at 200 characters before compiling.

Files changed

• backend/controllers/questionController.js — escapeRegex helper + literal, length-capped regex construction.
• backend/tests/questionController.redos.unit.test.js — tests that metacharacters are escaped, nested-quantifier patterns are neutralized, length is capped, and case-insensitivity is preserved.

Testing

npx vitest run tests/questionController.redos.unit.test.js — 5/5 passing. Full suite shows no new failures vs. the origin/main baseline.

Closes #1443

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📥 Commits

Reviewing files that changed from the base of the PR and between 8acb5b8 and 4d2ffc7.

📒 Files selected for processing (2)

• backend/controllers/questionController.js
• backend/tests/questionController.redos.unit.test.js

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