flask Automatically escape text in .svg files (Fix)

The Fix

Upgrade to version 2.2.3 or later.

Based on closed pallets/flask issue #4831 · PR/commit linked

Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.

Jump to Verify Open PR/Commit

@@ -9,6 +9,9 @@ Version 2.2.3
 Unreleased
 
+-   Autoescaping is now enabled by default for ``.svg`` files. Inside
+    templates this behavior can be changed with the ``autoescape`` tag.
+    :issue:`4831`

repro.py

<svg xmlns='http://www.w3.org/2000/svg'
    xmlns:xlink='http://www.w3.org/1999/xlink' width="250" height="220" viewBox="0 0 250 220">
    <text fill="#ffffff" font-family="Roboto, Segoe UI, Ubuntu, Arial, sans-serif" font-weight="600" font-size="15px">
        {{ title }}
    </text>
</svg>

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\nUpgrade to version 2.2.3 or later.\nWhen NOT to use: This fix should not be used if SVG files require manual escaping for specific use cases.\n\n

Why This Fix Works in Production

Trigger: In this example, trying to insert a title into an SVG to render, an error will occur if the title contains unescaped text such as an ampersand (eg. "TEST &…
Mechanism: Adds .svg to the list of file extensions that are autoescaped by default in Flask, addressing issue #4831.
Why the fix works: Adds .svg to the list of file extensions that are autoescaped by default in Flask, addressing issue #4831. (first fixed release: 2.2.3).

Production impact:

If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.

Why This Breaks in Prod

Production symptom (often without a traceback): In this example, trying to insert a title into an SVG to render, an error will occur if the title contains unescaped text such as an ampersand (eg. "TEST & EXAMPLE")

Proof / Evidence

GitHub issue: #4831
Fix PR: https://github.com/pallets/flask/pull/4840
First fixed release: 2.2.3
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.61

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“## Summary Currently, autoescaping is enabled for all templates ending in .html, .htm, .xml as well as .xhtml when using render_template() (https://flask.palletsprojects.com/en/2.2.x/templating/). As SVG files are very similar in nearly all”

Issue thread · issue description · source

Failure Signature (Search String)

In this example, trying to insert a title into an SVG to render, an error will occur if the title contains unescaped text such as an ampersand (eg. "TEST & EXAMPLE")

Copy-friendly signature

signature.txt

Failure Signature
-----------------
In this example, trying to insert a title into an SVG to render, an error will occur if the title contains unescaped text such as an ampersand (eg. "TEST & EXAMPLE")

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
In this example, trying to insert a title into an SVG to render, an error will occur if the title contains unescaped text such as an ampersand (eg. "TEST & EXAMPLE")

Minimal Reproduction

repro.py

<svg xmlns='http://www.w3.org/2000/svg'
    xmlns:xlink='http://www.w3.org/1999/xlink' width="250" height="220" viewBox="0 0 250 220">
    <text fill="#ffffff" font-family="Roboto, Segoe UI, Ubuntu, Arial, sans-serif" font-weight="600" font-size="15px">
        {{ title }}
    </text>
</svg>

What Broke

Rendering SVG templates with unescaped text resulted in errors and incorrect display.

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

Upgrade to version 2.2.3 or later.

When NOT to use: This fix should not be used if SVG files require manual escaping for specific use cases.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/pallets/flask/pull/4840

First fixed release: 2.2.3

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be used if SVG files require manual escaping for specific use cases.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
2.2.3	Fixed

Related Issues

No related fixes found.

Cluster: flask:configuration-error All hubs All clusters

Related clusters: Data consistency Other Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.